Chemically-sensitive field effect transistors, systems, and methods for manufacturing and using the same

ABSTRACT

An apparatus includes a biosensor integrated circuit (IC) chip with sensing zones and/or well structures configured to receive a liquid with biological analytes. The chip includes a passivation layer with an opening over a channel layer and an array of graphene field effect transistors (gFETs) individually having a 2D graphene channel disposed on a dielectric oxide layer, a conductive drain, and a conductive source. A liquid gate is formed above the top surface of the graphene channel. The chip further includes reference electrodes formed in a metal layer, configured to contact the liquid, and disposed at a horizontal distance apart from the graphene channels. The individual gFETs are operable to enable a set of measurements to sense parameters of the biological analytes based on changes in a shape of Id-Vgs transconductance curves. A system and a method have similar structures and perform the functions of the apparatus.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of andpriority to U.S. application Ser. No. 16/586,964, filed Sep. 28, 2019,which is a continuation of U.S. application Ser. No. 16/014,838, filedJun. 21, 2018, now patented U.S. Pat. No. 10,429,381, which is acontinuation of U.S. application Ser. No. 15/256,493, filed Sep. 2,2016, now patented U.S. Pat. No. 10,006,910, which is a continuation ofU.S. application Ser. No. 15/239,800, filed Aug. 17, 2016, now patentedU.S. Pat. No. 9,857,328. This application is also a continuation in partof U.S. Provisional patent application Ser. No. 16/302,550 filed May 16,2016, which in turn claims priority to U.S. Provisional PatentApplication No. 62/337,249, filed May 16, 2016.

Said U.S. application Ser. No. 15/256,493, filed Sep. 2, 2016, nowpatented U.S. Pat. No. 10,006,910, also claims benefit of and priorityto: U.S. Provisional Patent Application Ser. No. 62/213,112, filed Sep.2, 2015; U.S. Provisional Patent Application Ser. No. 62/213,117, filedSep. 2, 2015; U.S. Provisional Patent Application Ser. No. 62/213,151,filed Sep. 2, 2015; U.S. Provisional Patent Application Ser. No.62/214,850, filed Sep. 4, 2015; U.S. Provisional Patent Application Ser.No. 62/214,892, filed Sep. 4, 2015; U.S. Provisional Patent ApplicationSer. No. 62/214,901, filed Sep. 4, 2015; U.S. Provisional PatentApplication Ser. No. 62/214,912, filed Sep. 4, 2015; U.S. ProvisionalPatent Application Ser. No. 62/214,910, filed Sep. 4, 2015; U.S.Provisional Patent Application Ser. No. 62/215,018, filed Sep. 6, 2015.

Said U.S. application Ser. No. 15/239,800, filed Aug. 17, 2016, nowpatented U.S. Pat. No. 9,857,328, is a continuation in part of U.S.application Ser. No. 15/225,764 filed Aug. 1, 2016, now patented U.S.Pat. No. 10,020,300. Said U.S. application Ser. No. 15/239,800, filedAug. 17, 2016 claims benefit of and priority to: U.S. Provisional PatentApplication Ser. No. 62/205,803, filed Aug. 17, 2015; U.S. ProvisionalPatent Application Ser. No. 62/205,808, filed Aug. 17, 2015; U.S.Provisional Patent Application Ser. No. 62/206,166, filed Aug. 17, 2015;U.S. Provisional Patent Application Ser. No. 62/206,224, filed Aug. 17,2015; U.S. Provisional Patent Application Ser. No. 62/206,228, filedAug. 17, 2015; U.S. Provisional Patent Application Ser. No. 62/206,372,filed Aug. 18, 2015; U.S. Provisional Patent Application Ser. No.62/206,814, filed Aug. 18, 2015.

Said U.S. application Ser. No. 15/225,764, filed Aug. 1, 2016, is also acontinuation in part of U.S. Application Ser. No. 15/065,744, filed Mar.9, 2016, now patented U.S. Pat. No. 9,618,474, which in turn claimsbenefit of U.S. Provisional Patent Application Ser. No. 62/130,598,filed Mar. 9, 2015; U.S. Provisional Patent Application Ser. No.62/130,594, filed Mar. 9, 2015; U.S. Provisional Patent Application Ser.No. 62/130,601, filed Mar. 9, 2015; U.S. Provisional Patent ApplicationSer. No. 62/130,621, filed Mar. 10, 2015.

Said U.S. application Ser. No. 15/225,764, filed Aug. 1, 2016, is also acontinuation in part of U.S. application Ser. No. 15/065,744, filed Mar.9, 2016, now patented U.S. Pat. No. 9,618,474, which in turn, is acontinuation in part of U.S. application Ser. No. 14/963,253, filed Dec.9, 2015. U.S. application Ser. No. 15/225,764, filed Aug. 1, 2016, isalso a continuation in part of U.S. application Ser. No. 15/182,533.

Said U.S. application Ser. No. 15/182,533, filed Jun. 14, 2016, nowpatented U.S. Pat. No. 9,859,394, in turn claims benefit of U.S.Provisional Patent Application Ser. No. 62/175,351, filed Jun. 14, 2015.

Said U.S. application Ser. No. 14/963,253, filed Dec. 9, 2015, in turnclaims benefit of U.S. Provisional Patent Application Ser. No.62/094,016, filed Dec. 18, 2014; U.S. Provisional Patent ApplicationSer. No. 62/130,594, filed Mar. 9, 2015; U.S. Provisional PatentApplication Ser. No. 62/199,987, filed Aug. 1, 2015; and U.S.Provisional Patent Application Ser. No. 62/206,228, filed Aug. 17, 2015.

For all permissible purposes, the disclosures of each of the aboveapplications are incorporated herein by reference.

FIELD

The present disclosure generally relates to field effect transistors andmethods of making and using the same for the analysis of biological orchemical materials or reactions and bioinformatics processing. Morespecifically, the present disclosure relates to two-dimensionalnanomaterial-based field effect transistors useful for chemical andbiological analysis.

BACKGROUND

Certain types of transistor-based sensors have been described as usefulfor sensing applications. However, various existing designs have limitedsensitivity and scalability.

SUMMARY

An apparatus includes a biosensor integrated circuit (IC) chip havingone or more sensing zones within one or more well structures configuredto receive a liquid comprising one or more biological analytes. The chipincludes a passivation layer with an opening over a channel layer andincluding an array of graphene field effect transistors (gFETs). Theindividual gFETs include a graphene channel formed in the channel layerand form in a two-dimensional layer of carbon atoms, the graphenechannel disposed on a dielectric oxide layer. A conductive drain isconnected at a first end of the graphene channel and a conductive issource connected at a second end of the graphene channel. A liquid gateis formed above the top surface of the graphene channel upon receipt ofthe liquid. The biosensor IC chip further includes one or more referenceelectrodes formed in a metal layer of the biosensor IC chip andconfigured to contact the liquid, the one or more reference electrodesdisposed at a horizontal distance apart from the graphene channels ofthe gFETs in the array, where at least one of the one or more referenceelectrodes is configured to apply a liquid gate voltage to the liquidand at least one of the one or more reference electrodes is configuredto measure a liquid gate voltage of the liquid. The individual gFETs andthe first and second reference electrodes are operable to enable a setof measurements to be made to sense one or more parameters of abiological analyte in the liquid based on changes in a shape of achemical sensing Id-Vgs curve relative to a reference Id-Vgs, inresponse to the presence of the biological analyte in the liquid on orover the channels of the individual gFETs.

In various example implementations, changes in the shape of the chemicalsensing Id-Vgs curve relative to a reference Id-Vgs curves includetransconductance slope changes. In some examples, the transconductanceslope changes include changes to transconductance slope in both a p-typeregion and an n-type region of the chemical sensing Id-Vgs curve. Incertain examples, the individual gFETs are configured to enable sensingof one or more parameters of the one or more biological analytes in theliquid based on shifts of a chemical sensing Id-Vgs curve relative to areference Id-Vgs. In one or more examples, shifts of the chemicalsensing Id-Vgs curve relative to a reference Id-Vgs are selected fromhorizontal shifts, vertical shifts, or combinations thereof. In someexamples, shifts of the chemical sensing Id-Vgs curve relative to areference Id-Vgs include shifts in parameters selected from on current(Ion) in the p-type region, Dirac voltage (VDirac), on current (Ion) inthe n-type region, and combinations thereof.

In some examples, the chip includes one or more capture regions on orover the channel of the one or more gFETs, the individual captureregions configured respectively to accommodate attachment of a selectedbiomaterial to a top surface of the graphene channel, the biomaterialselected to detect a biological analyte of the one or more biologicalanalytes in the liquid. In certain examples, the biomaterials in therespective capture regions of the one or more capture regions areselected to detect analytes selected from ions associated withbiomolecules, nucleic acids, antigens, polysaccharides, proteins,peptides, small molecules, and combinations thereof. In certainimplementations, at least a portion of the source electrodes and thedrain electrodes have interdigitated geometries. In some examples, thepassivation layer provides an insulating layer between liquid and theregions at which the source electrode and the drain electrode connect tothe graphene channel of the individual gFETs. In certain examples, thepassivation layer includes silicon nitride. In various examples, an ionpermeable membrane is disposed above the graphene channel and configuredto allow selected ions to pass to the sensing region of the graphenechannel. In certain implementations, flow channels bring reagents and/oranalytes to the one or more well structures.

A system comprising further includes a processor configured to readdigitized signals from the individual gFETs to respectively determineone or more parameters of the one or more biological analytes in theliquid based on changes in the shape of the chemical sensing Id-Vgscurve relative to the reference Id-Vgs, in response to the presence ofthe analyte in the liquid on or over the graphene channel of theindividual gFETs.

A method includes providing a biosensor integrated circuit (IC) chiphaving a plurality of well structures configured to receive a liquidthat includes one or more biological analytes, the chip includes apassivation layer with an opening over one or more graphene field effecttransistors (gFETs) corresponding to the well structure, the individualgFETs include a graphene channel comprising a two-dimensional layer ofcarbon atoms, a capture region on or over the graphene channel andconfigured to selectively capture a first analyte or a second analyte ofthe one or more biological analytes. The gFETs also include a conductivedrain connected to a first end of the graphene channel and a conductivesource connected to a second end of the graphene channel. The biosensorIC chip further includes one or more reference electrodes formed incorresponding metal layer portions of the biosensor IC chip and disposedat a horizontal distance apart from the graphene channels of the one ormore gFETs and configured to apply and/or measure a liquid gate voltageto a liquid confined above a top surface of the graphene channels.

The method includes sensing one or more parameters of the one or moreanalytes in the liquid based on changes in a shape of a chemical sensingId-Vgs curve relative to a reference Id-Vgs, in response to the presenceof the first analyte or the second analyte in the liquid gate beingcaptured on or over the graphene, and determining differences betweenthe first analyte and the second analyte based on transconductance slopedifferences of the respective chemical sensing Id-Vgs curves.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the disclosure will be readilyunderstood, a more particular description of the examples brieflydescribed above will be rendered by reference to specific examples thatare illustrated in the appended drawings. Understanding that thesedrawings depict only typical examples of the subject matter and are nottherefore to be considered to be limiting of its scope, the subjectmatter will be described and explained with additional specificity anddetail through the use of the accompanying drawings.

FIG. 1A is a side sectional illustration of an ISFET device fabricatedusing traditional semiconductor FET transistor technology for the sensortransistor.

FIG. 1B is a side sectional illustration of a substrate for use in aChemFET, such as for a system for analysis of biological and/or chemicalmaterials. In this instance, the substrate includes a dielectric layerhaving a source and a drain, and further includes a sensing zone havinga graphene nanomaterial layer associated therewith.

FIG. 1C is a top-down illustration of a substrate for use in a ChemFET,such as for a system for analysis of biological and/or chemicalmaterials. In this instance, the substrate includes a dielectric layerhaving a source and a drain, and further includes a sensing zone havinga graphene nanomaterial layer associated therewith.

FIG. 1D is an illustration of a graphene nanomaterial, such as for usein the substrate of FIG. 1C.

FIG. 1E is an illustration of molybdenum disulfide nanomaterial.

FIG. 1F is an illustration of black phosphorous or phosphorenenanomaterial in which the upper illustration is a top-down view and thelower illustration is a side view of the nanomaterial.

FIG. 1G is an illustration of silicon in its crystalline state.

FIG. 1H is an illustration of a carbon nanotube (CNT).

FIG. 1I is an illustration of a semiconductor nanowire (NW) structureformed as nanowire.

FIG. 1J is an illustration of a semiconductor nanowire (NW) structureformed from a bulk semiconductor layer.

FIG. 1K is an illustration of a transistor included of a semiconductornanowire (NW) and including a gate, gate dielectric and source and draincontacts.

FIG. 1L is a side sectional illustration, along section X-X of FIG. 1K,of a semiconductor nanowire transistor configured as a MOSFET.

FIG. 1M is a side sectional illustration, along section X-X of FIG. 1K,of a semiconductor nanowire transistor configured as a Schottky BarrierFET.

FIG. 1N is a side sectional illustration, along section X-X of FIG. 1K,of a semiconductor nanowire transistor configured as a junctionless FET.

FIG. 1O is a side sectional illustration, along section X-X of FIG. IK,of a semiconductor nanowire transistor configured as a Tunnel FET.

FIG. 1P is a side sectional illustration of a graphene layered substrateof FIG. 1C configured as a ChemFET having an analyte orreaction-sensitive layer associated with the graphene layer, such as foruse in a system for analysis of biological and/or chemical materials.

FIG. 2A is an illustration of a ChemFET having a graphene layered wellstructure, such as for a system for analysis of biological and/orchemical materials.

FIG. 2B is an illustration of a ChemFET of FIG. 2A, having a graphenelayered well structure that further includes a sensing layer associatedwith the graphene layer, such as for a system for analysis of biologicaland/or chemical materials.

FIG. 2C is a top plan view of a ChemFET with a well structure.

FIG. 2D is a top plan view of a ChemFET with another configuration of awell structure.

FIG. 3A is a side sectional view of a ChemFET with a solution gate.

FIG. 3B is an illustration of a ChemFET, having a graphene layered wellstructure that includes a sensing layer associated with the graphenelayer, which further includes a microbead therein with DNA templates forDNA sequencing.

FIG. 3C is an illustration of a ChemFET, having a graphene layered wellstructure that includes a sensing layer associated with the graphenelayer, which further includes DNA templates deposited on the sensinglayer for DNA sequencing.

FIG. 3D is an illustration of a ChemFET, having a graphene layered wellstructure that includes a sensing layer associated with the graphenelayer, which further includes antibodies associated with the sensinglayer for detection of antigens.

FIG. 3E is an illustration of a ChemFET, having a graphene layered wellstructure that includes a sensing layer associated with the graphenelayer, which further includes a cell to be monitored for cell activity.

FIG. 3F is an illustration highlighting a second analyte orreaction-sensitive layer coating the walls of a well.

FIG. 4A is an illustration of a ChemFET with a graphene layered wellstructure and having a permeable membrane associated with the graphenelayer.

FIG. 4B is an illustration of a ChemFET with a graphene layered wellstructure and having an ion getter associated with the ChemFET.

FIG. 4C is an illustration of a ChemFET with a graphene layered wellstructure and having a charge trap screening layer associated with thechannel.

FIG. 5A shows electrodes overplated in trenches in an oxide layer.

FIG. 5B shows a side sectional view of electrodes in a dielectric layerafter chemical-mechanical planarization (CMP) process. The CMP processpartially etches part of the dielectric layer to allow the electrodes toproject above the surface of the dielectric layer.

FIG. 5C shows a side sectional view of electrodes in a dielectric layerthat have additional material in the form of plated bumps on the contactregion of the electrodes.

FIG. 5D shows a side sectional view of an electrode in a dielectriclayer with a graphene layer on top of the electrode and bump materialextending through holes in the graphene layer.

FIG. 5E shows top-down view of the electrode and graphene channelstructure of FIG. 5D.

FIG. 5F shows a side sectional view of an example of a top electrode anda bottom electrode sandwiching a graphene layer from above and below,and Furthermore, portions of the electrode project through holes thegraphene layer at several intended locations. The structure providestop, bottom and edge contact between the electrode and the graphene,

FIG. 5G is an illustration of various planar source and drain electrodedesigns, including interdigitated designs.

FIG. 5H is an illustration of using the well walls to create 3Dinterdigitated electrodes.

FIG. 5I is an illustration of the well structure of FIG. 5H andincluding a nanomaterial that covers a sidewall and underlying sourceand drain electrodes.

FIG. 5K is an illustration of a well that uses carbon nanotubes tocreate interdigitated transistors in a vertical direction.

FIG. 5L is an illustration of a top plane view of a source and drainelectrodes at the bottom of a well.

FIG. 5M is an illustration of using alternating vertical metal layers tocreate an interdigitated type of effect to maximize the of ratio channelwidth to channel length.

FIG. 5N is an illustration of the structure of FIG. 5M with a transistormaterial or an analyte or reaction-sensitive layer.

FIGS. 6A-6K illustrate using alternating vertical layers of metal andtransistor material to create an interdigitated type of effect tomaximize the ratio of channel width to channel length and the processsteps used to achieve that structure.

FIG. 7A is a solution-gated ChemFET.

FIG. 7B is an illustration of a ChemFET with multiple enhancementsincluding a local backgate electrode in concert with a solution gate toprovide a dual gate ChemFET.

FIG. 7C is a graph of an average sensitivity of a graphene FET (“gFET”)calculated as a function of liquid gate potential.

FIG. 8 is a side sectional view of a ChemFET with several improvementscombined in one example.

FIG. 9A is an illustration of a CMOS wafer with a graphene layerdeposited on exposed metal electrodes and dielectric surface.

FIG. 9B is an illustration of etching the dielectric under the graphenechannel.

FIG. 9C is an illustration of using the fluid to create a gate allaround a suspended graphene channel.

FIG. 9D shows a top view of the gate all around ChemFET shown in FIG.9C.

FIG. 10A is an illustration of a CMOS wafer with a graphene layerdeposited on exposed metal electrodes.

FIG. 10B is an illustration of etching the dielectric under the graphenechannel and under the metal electrode.

FIG. 10C is an illustration of etching the metal under the graphene tocreate a gate all around a suspended graphene channel.

FIG. 11A is an illustration of a CMOS wafer with a graphene layerdeposited on exposed metal electrodes and a dielectric surface.

FIG. 11B is an illustration of etching the dielectric under the graphenewith an isotropic etch process to create a gate all around a suspendedgraphene channel.

FIG. 12 is an illustration of multiple chemically-sensitive field-effecttransistors with a well structures and reference electrodes on top ofthe wells.

FIG. 13A is a graph of an I_(d)-V_(gs) curve with characteristics thatare used to categorize I_(d)-V_(gs) curves.

FIG. 13B is a graph of an I_(d)-V_(gs) curve illustrating a singledifference or multiple differences.

FIG. 13C is a graph of an I_(d)-V_(gs) curve illustrating a shift in theI_(d)-V_(gs) curve.

FIG. 13D is a graph of an I_(d)-V_(gs) curve illustrating a change inthe shape of the I_(d)-V_(gs) curve.

FIG. 13E is a graph of an I_(d)-V_(gs) curve illustrating a change inthe level of the I-Vg curve (Ion in p-type region).

FIG. 13F is a graph of an I_(d)-V_(gs) curve illustrating a change inthe level of the I_(d)-V_(gs) curve (Ion in n-type region).

FIG. 13G is a graph of an I_(d)-V_(gs) curve illustrating a change inthe level of the I_(d)-V_(gs) curve (I_(OFF)).

FIG. 13H is a graph of an I_(d)-V_(gs) curve illustrating a fitpolynomial or other fitting line to curve and use coefficients as readcriterion.

FIG. 13I is a graph of an I_(d)-V_(gs) curve illustrating a slope of theI_(d)-V_(gs) curve on one or both sides and use of a solution gate andback gate in combination to improve a signal and move the curve wheredesired.

FIG. 14A is an illustration of an exemplary graphene field-effecttransistor chip.

FIG. 14B is a graph of an I_(d)-V_(gs) curve for various pH values.

FIG. 14C is a graph of current increase vs. pH increase.

FIG. 14D is a graph of frequency vs. normalized power spectral densityfor silicon ISFET.

FIG. 14E is a graph of frequency vs. normalized power spectral densityfor a typical graphene FET.

FIG. 14F is a graph of frequency vs. normalized power spectral densityfor a graphene FET of the present disclosure.

FIG. 14G is a graph of noise vs. bias voltage.

FIG. 14H is a graph of Dirac voltage vs. current increase.

FIG. 15A is a top plan view of a sensor array IC for a system foranalysis of biological or chemical materials, where the sensor arrayincludes multiple chemically-sensitive field-effect transistors.

FIG. 15B depicts a ChemFET sensor IC chip.

FIG. 15C is a block diagram of a system for analysis of biological orchemical materials.

FIG. 15D is a block diagram of a circuitry component for a system foranalysis of biological or chemical materials.

FIG. 15E is a block diagram of a computing component for a system foranalysis of biological or chemical materials.

FIG. 15F is a block diagram of components for a system for analysis ofbiological or chemical materials.

FIG. 16 depicts a stack of electrically connected IC chips, including aChemFET sensor IC chip and one or more other IC chips such as aprocessor or memory IC chip.

FIG. 17A depicts face to face stacked ChemFET sensor IC chips definingflow channels.

FIG. 17B depicts face to face stacked ChemFET sensor IC chips with theirorientation provided by external members.

FIG. 17C depicts face up stacked ChemFET sensor IC chips and a packagelid that together define fluid flow channels.

FIG. 18A is an illustration of a ChemFET having a graphene layered wellstructure that includes a microbead therein.

FIG. 18B is an illustration of a ChemFET, having a graphene layered wellstructure and an ion-sensitive layer over the graphene, that includes amicrobead therein.

FIG. 18C is an illustration of a ChemFET having a graphene layered wellstructure that includes a plurality of microbeads therein.

FIG. 19A is an illustration of the substrate of FIG. 2B, having asilicon dioxide layer positioned above a graphene layered sensing zone,and utilizing a magnetic field for the positioning of a nano- ormicrobead to be associated therewith.

FIG. 19B is an illustration of the substrate of FIG. 2B, having asilicon dioxide layer positioned above a graphene layered sensing zone,and utilizing a magnetic field for the positioning of a nano- ormicrobead to be associated therewith.

FIG. 19C is an illustration of the substrate of FIG. 19B, in analternate configuration, such as utilizing a magnetic field reversal ofa magnet to release a nano- or microbead.

FIG. 19D is an illustration of the ChemFET of FIG. 2B, such as for asystem for analysis of biological or chemical materials, utilizing anelectric field for positioning of a nano- or microbead.

FIG. 19E is an illustration of an array of ChemFETs for a system foranalysis of biological or chemical materials utilizing multiple magnetsfor generating a plurality of magnetic fields for positioning of nano-or microbeads within the wells.

FIG. 20A is an illustration of electrowetting for biomoleculeattachment.

FIG. 20B is an illustration of electrophoresis for biomoleculeattachment.

FIG. 20C is an illustration of microfluidics for biomolecule attachment.

FIG. 20D is an illustration of an optical readout of DNA sequencingusing nanomaterials.

FIG. 21 is an illustration of an exemplary fabrication method as hereindescribed.

FIG. 22A illustrates a graphene growth step of direct bond transfer viaVan der Waals forces, in accordance with the method steps set forth inFIG. 21.

FIG. 22B illustrates a wafer-flipping step of direct bond transfer viaVan der Waals forces.

FIG. 22C illustrates a ROIC alignment step of direct bond transfer viaVan der Waals forces.

FIG. 22D illustrates a bonding graphene to an oxide on the ROIC waferstep of direct bond transfer via Van der Waals forces.

FIG. 22E illustrates a use of water electrolysis to create hydrogenbubbles to separate the graphene from the growth platform.

FIG. 22F illustrates a growth substrate removal step of direct bondtransfer via Van der Waals forces.

FIG. 23A illustrates a graphene growth step of direct bond transfer viafusion bonding.

FIG. 23B illustrates a deposit cover material and CMP or polish surfacestep of direct bond transfer via fusion bonding.

FIG. 23C illustrates a wafer-flipping step of direct bond transfer viafusion bonding.

FIG. 23D illustrates a ROIC preparation and ROIC alignment step ofdirect bond transfer via fusion bonding.

FIG. 23E illustrates a bonding a cover material to a ROIC wafer topinsulator step of direct bond transfer via fusion bonding.

FIG. 23F illustrates a growth substrate removal from the ROIC wafer,leaving the graphene on the ROIC step of direct bond transfer via fusionbonding.

FIG. 24A illustrates a graphene growth step of direct bond transfer viafusion bonding.

FIG. 24B illustrates an ion-sensitive oxide formed on the graphene layeron a growth wafer.

FIG. 24C illustrates a temporary bonding of the ion-sensitive oxide to ahandle wafer.

FIG. 24D illustrates a release of the graphene layer from the growthwafer.

FIG. 24E illustrates a deposit of a cover material and CMP or polishsurface step prior to direct bond transfer via fusion bonding.

FIG. 24F illustrates a wafer-flipping and ROIC aligning step of directbond transfer via fusion bonding.

FIG. 24G illustrates a bonding a cover material to a ROIC wafer topinsulator step of direct bond transfer via fusion bonding.

FIG. 24H illustrates a handle substrate removal from the ROIC wafer,leaving the graphene, covered by an ion-sensitive layer, on the ROICstep of direct bond transfer via fusion bonding.

FIG. 25 illustrates a bubble release process for a graphene layer fromits growth substrate aided by a through silicon via.

FIG. 26A illustrates a graphene with channels or divots for water accessand more efficient bubble transfer growth step of direct bond transfervia Van der Waals forces, in accordance with the method steps set forthin FIG. 21.

FIG. 26B illustrates a wafer-flipping step of direct bond transfer viaVan der Waals forces.

FIG. 26C illustrates a ROIC alignment step of direct bond transfer viaVan der Waals forces.

FIG. 26D illustrates a bonding graphene to an oxide on the ROIC waferstep of direct bond transfer via Van der Waals forces.

FIG. 26E illustrates a use of water electrolysis to create hydrogenbubbles to separate the graphene from the growth platform step of directbond transfer via Van der Waals forces.

FIG. 26F illustrates a growth substrate removal step of direct bondtransfer via Van der Waals forces.

FIG. 27 illustrates a Langmuir Blodgett deposition process as analternative option for the bubble release steps of FIG. 21.

FIG. 28A illustrates a controlled immersion and bubble release step ofthe alternative option for the bubble release step of FIG. 21.

FIG. 28B illustrates a graphene and PMMA fully released step of thealternative option for the bubble release step of FIG. 21.

FIG. 28C illustrates a drain solution (while the graphene is aligned tothe wafer) to transfer a layer onto a target step of the alternativeoption for the bubble release step of FIG. 21.

FIG. 29A illustrates a glass carrier preparation step of an adhesivetemporary bond material process.

FIG. 29B illustrates room temperature ultraviolet energy bonding step ofan adhesive temporary bond material process.

FIG. 29C illustrates an optional thin silicon wafer growth step of anadhesive temporary bond material process.

FIG. 29D illustrates a bonding the graphene layer to the target step ofan adhesive temporary bond material process.

FIG. 29E illustrates a laser glass release step of an adhesive temporarybond material process.

FIG. 29F illustrates an apply tape step of an adhesive temporary bondmaterial process.

FIG. 29G illustrates a peel off the adhesive material step of anadhesive temporary bond material process.

FIG. 30 illustrates an adhesive temporary bond material process.

FIG. 31 illustrates an adhesive temporary bond material process

FIG. 32A illustrates a nickel deposition on a graphene layer step of anadhesive temporary bond process with a nickel deposition layer.

FIG. 32B illustrates a tape lamination step of an adhesive temporarybond process with a nickel deposition layer.

FIG. 32C illustrates a tape peel and graphene transfer step of anadhesive temporary bond material process with a nickel deposition layer.

FIG. 32D illustrates a peel tape from the nickel layer step of anadhesive temporary bond material process with a nickel deposition layer.

FIG. 32E illustrates a wet etch to remove the nickel layer step of anadhesive temporary bond material process with a nickel deposition layer.

FIG. 33A shows a side sectional view of a semiconductor substrate coatedwith an insulated dielectric layer during fabrication of a ChemFET ofthe disclosure.

FIG. 33B illustrates a side sectional view of a conductive materiallayer on an insulated dielectric layer during fabrication of a ChemFETof the disclosure.

FIG. 33C shows a side sectional view of a patterned conductive materiallayer during fabrication of a ChemFET of the disclosure.

FIG. 33D illustrates a side sectional view of a 1D or 2D nanomateriallayer applied over electrodes during fabrication of a ChemFET of thedisclosure.

FIG. 33E shows a side sectional view of an analyte or reaction-sensitivelayer applied over a 1D or 2D nanomaterial layer during fabrication of aChemFET of the disclosure.

FIG. 33F illustrates a side sectional view of analyte orreaction-sensitive and 1D or 2D nanomaterial layers that have beenpatterned during fabrication of a ChemFET of the disclosure.

FIG. 33G shows a top-down view of an analyte or reaction-sensitivelayer, a conductive material layer and an insulated dielectric layerduring fabrication of a ChemFET of the disclosure.

FIG. 33H shows a side sectional view of an integrated circuit with aninsulating passivation layer during the process of forming a wellproximate the integrated circuit.

FIG. 33I illustrates a side sectional view of an integrated circuit witha patterned insulating passivation layer during the process of forming awell proximate the integrated circuit.

FIG. 34A illustrates a graphene on a ROIC wafer step of a CMOSintegration method.

FIG. 34B illustrates a patterning a graphene layer to form channels stepof a CMOS integration method.

FIG. 34C illustrates a depositing an etch stop layer over a graphenelayer to step of a CMOS integration method.

FIG. 34D illustrates a deposit, pattern and etch a thick insulator layerstep of a CMOS integration method.

FIG. 34E illustrates a wet etch ESL, pattern and DRIE oxide overinterconnects step of a CMOS integration method.

FIG. 34F illustrates a deposit a barrier, liner, copper plate, CMP stepof a CMOS integration method.

FIG. 34G illustrates a deposit a barrier/adhesion layer, depositaluminum, pattern, etch aluminum interconnect and pad layer step of aCMOS integration method.

FIG. 34H illustrates a deposit Si0₂ (e.g., CVD), CMP, pad open etch stepof a CMOS integration method.

FIG. 34I illustrates a DRIE well insulator down to an etch stop layerstep of a CMOS integration method.

FIG. 34J illustrates a wet etch a thin etch stop layer step of a CMOSintegration method.

FIG. 35A is an illustration of an oxide etching step for well formationon a gFET according to the disclosure.

FIG. 35B is an illustration of a graphene placement step for wellformation on a gFET according to the disclosure.

FIG. 35C is an illustration of a graphene patterning step for wellformation on a gFET according to the disclosure.

FIG. 36A is an illustration of nanoimprinting of a polymer material forwell formation on a gFET according to the disclosure.

FIG. 36B is an illustration of nanoimprinting of a polymer material forwell formation on a gFET according to the disclosure.

FIG. 36C is an illustration of nanoimprinting of a polymer material forwell formation on a gFET according to the disclosure.

FIG. 36D is an illustration of nanoimprinting of a polymer material forwell formation on a gFET according to the disclosure.

FIG. 37A is an illustration of an analyte sensitive layer or otherfunctional layer placement on a graphene layer step for well formationon a gFET according to the disclosure.

FIG. 37B is an illustration of placement of a thin inorganic layer (etchstop layer) on the functional layer step for well formation on a gFETaccording to the disclosure.

FIG. 37C is an illustration of a dry etch the thick inorganic layer stepfor well formation on a gFET according to the disclosure.

FIG. 37D is an illustration of a wet or gaseous etch the thin inorganiclayer step for well formation on a gFET according to the disclosure.

FIG. 38A is a ChemFET sensor IC chip with ions flowing between chambers.

FIG. 38B is a ChemFET sensor IC chip with a moveable fluid seal in anupper position.

FIG. 38C is a ChemFET sensor IC chip with a moveable fluid seal in asealed position.

FIG. 38D is a ChemFET sensor IC chip with a barrier generator andelectromagnet barrier fields.

FIG. 38E is a ChemFET sensor IC chip with a flow control memberincluding microvalves.

FIG. 39 is a ChemFET sensor IC chip with coordinated bitlinesegmentation and fluid flow control to reduce read latency and improveread accuracy.

DETAILED DESCRIPTION

Reference throughout this specification to “one example,” “an example,”or similar language means that a particular feature, structure, orcharacteristic described in connection with the example is included inat least one example. Thus, appearances of the phrases “in one example,”“in an example,” and similar language throughout this specification may,but do not necessarily, all refer to the same example, but mean “one ormore but not all examples” unless expressly specified otherwise. Theterms “including,” “comprising,” “having,” and variations thereof mean“including but not limited to” unless expressly specified otherwise. Anenumerated listing of items does not imply that any or all of the itemsare mutually exclusive and/or mutually inclusive, unless expresslyspecified otherwise. The terms “a,” “an,” and “the” also refer to “oneor more” unless expressly specified otherwise.

Furthermore, the described features, structures, or characteristics ofthe disclosure may be combined in any suitable manner in one or moreexamples. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of examples of the subject matter. One skilled inthe relevant art will recognize, however, that the claims may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the disclosure.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one example of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

Reference throughout this specification to “one example,” “an example,”or similar language means that a particular feature, structure, orcharacteristic described in connection with the example is included inat least one example. Thus, appearances of the phrases “in one example,”“in an example,” and similar language throughout this specification may,but do not necessarily, all refer to the same example, but mean “one ormore but not all examples” unless expressly specified otherwise. Theterms “including,” “comprising,” “having,” and variations thereof mean“including but not limited to” unless expressly specified otherwise. Anenumerated listing of items does not imply that any or all of the itemsare mutually exclusive and/or mutually inclusive, unless expresslyspecified otherwise. The terms “a,” “an,” and “the” also refer to “oneor more” unless expressly specified otherwise.

Furthermore, the described features, advantages, and characteristics ofthe examples may be combined in any suitable manner. One skilled in therelevant art will recognize that the examples may be practiced withoutone or more of the specific features or advantages of a particularexample. In other instances, additional features and advantages may berecognized in certain examples that may not be present in all examples.

These features and advantages of the examples will become more fullyapparent from the following description and appended claims, or may belearned by the practice of examples as set forth hereinafter. As will beappreciated by one skilled in the art, aspects of the present disclosuremay be embodied as a system, method, and/or computer program product.Accordingly, aspects of the present disclosure may take the form of anentirely hardware example, an entirely software example (includingfirmware, resident software, micro-code, etc.) or an example combiningsoftware and hardware aspects that may all generally be referred toherein as a “circuit,” “module,” or “system.” Furthermore, aspects ofthe present disclosure may take the form of a computer program productembodied in one or more computer readable medium(s) having program codeembodied thereon.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of program code may, forinstance, include one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may includedisparate instructions stored in different locations which, when joinedlogically together, include the module, and achieve the stated purposefor the module.

Indeed, a module of program code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.Where a module or portions of a module are implemented in software, theprogram code may be stored and/or propagated on in one or more computerreadable medium(s).

The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present disclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (“RAM”), aread-only memory (“ROM”), an erasable programmable read-only memory(“EPROM” or Flash memory), a static random access memory (“SRAM”), aportable compact disc read-only memory (“CD-ROM”), a digital versatiledisk (“DVD”), a memory stick, a floppy disk, a mechanically encodeddevice such as punch-cards or raised structures in a groove havinginstructions recorded thereon, and any suitable combination of theforegoing. A computer readable storage medium, as used herein, is not tobe construed as being transitory signals per se, such as radio waves orother freely propagating electromagnetic waves, electromagnetic wavespropagating through a waveguide or other transmission media (e.g., lightpulses passing through a fiber-optic cable), or electrical signalstransmitted through a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may includecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (“ISA”) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (“LAN”) or a wide areanetwork (“WAN”), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some examples, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (“FPGA”),or programmable logic arrays (“PLA”) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to examples of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general-purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein includes anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of program instructions may,for instance, include one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may includedisparate instructions stored in different locations which, when joinedlogically together, include the module, and achieve the stated purposefor the module.

The schematic flowchart diagrams and/or schematic block diagrams in theFigures illustrate the architecture, functionality, and operation ofpossible implementations of apparatuses, systems, methods, and computerprogram products according to various examples of the presentdisclosure. In this regard, each block in the schematic flowchartdiagrams and/or schematic block diagrams may represent a module,segment, or portion of code, which includes one or more executableinstructions of the program code for implementing the specified logicalfunction(s).

It should also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. Other steps and methods may be conceived that are equivalentin function, logic, or effect to one or more blocks, or portionsthereof, of the illustrated Figures.

Although various arrow types and line types may be employed in theflowchart and/or block diagrams, they are understood not to limit thescope of the corresponding examples. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the depictedexample. For instance, an arrow may indicate a waiting or monitoringperiod of unspecified duration between enumerated steps of the depictedexample. It will also be noted that each block of the block diagramsand/or flowchart diagrams, and combinations of blocks in the blockdiagrams and/or flowchart diagrams, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and program code.

As used herein, a list with a conjunction of “and/or” includes anysingle item in the list or a combination of items in the list. Forexample, a list of A, B, and/or C includes only A, only B, only C, acombination of A and B, a combination of B and C, a combination of A andC or a combination of A, B and C. As used herein, a list using theterminology “one or more of” includes any single item in the list or acombination of items in the list. For example, one or more of A, B and Cincludes only A, only B, only C, a combination of A and B, a combinationof B and C, a combination of A and C or a combination of A, B and C. Asused herein, a list using the terminology “one of” includes one and onlyone of any single item in the list. For example, “one of A, B, and C”includes only A, only B, or only C and excludes combinations of A, B,and C. As used herein, “a member selected from the group consisting ofA, B, and C,” includes one and only one of A, B, or C, and excludescombinations of A, B, and C.” As used herein, “a member selected fromthe group consisting of A, B, and C and combinations thereof” includesonly A, only B, only C, a combination of A and B, a combination of B andC, a combination of A and C or a combination of A, B and C.

Glossary and Abbreviations

Unless otherwise noted, or as may be evident from the context of theirusage, any terms, abbreviations, acronyms or scientific symbols andnotations used herein are to be given their ordinary meaning in thetechnical discipline to which the disclosure most nearly pertains. Thefollowing terms, abbreviations and acronyms may be used throughout thedescriptions presented herein and should generally be given thefollowing meaning unless contradicted or elaborated upon by otherdescriptions set forth herein.

ChemFET: a Chemically-Sensitive Field Effect Transistor (FET),

CMOS: Complementary Metal Oxide Semiconductor;

CNT: carbon nanotube, a type of 1D nanomaterial formed of carbon atomsarranged in a tube-like structure that has a small cross-section area incomparison to its length;

Damascene: a fabrication process whereby a trench is formed first in adielectric material and then the trench is filled with a conductivematerial in a second process step;

DNA: deoxyribonucleic acid;

ESL: Etch Stop Layer, a layer upon which an etching process may stop orbe significantly attenuated;

FET: a Field Effect Transistor;

GAA: Gate All-Around, a transistor gate structure wherein the gatesurrounds a portion of the channel;

gFET: a FET with a graphene nanomaterial channel;

I: current. If there is a subscript, such as I_(d) (sometimes typed asId), the subscript indicates the location at which the current isflowing (e.g., I_(d) is the current flow at the transistor drain);

IC: an Integrated Circuit, ISFET: and Ion Sensitive FET;

MOSFET: a Metal Oxide Semiconductor Field Effect Transistor;

Nanomaterial: a material in which at least one principal dimension(e.g., length, thickness, width) is in the range of 1 to 100 nanometers;

NGS: Next Generation Sequencing;

NW: nanowire, a 1D nanomaterial that has a small cross-section area incomparison to its length;

Passivation: the topmost or final insulating protective layer on an ICchip

RNA: ribonucleic acid;

ROIC: Read-Out Integrated Circuit is circuitry that assists with readingout signals from a sensor or sensor array and may include such circuitsas analog to digital converters, amplifiers, filters, row or columndecoders, sample and hold circuits and the like;

SNP: Single Nucleotide Polymorphism;

V: voltage. If there is a subscript, such as V_(gs) (sometimes typed asVgs), the subscript indicates between which points or locations thevoltage potential is defined (e.g., V_(gs) is the voltage between thegate and source of a transistor).

Introduction and Overview

In some aspects, the present disclosure addresses the shortcomings ofconventional NGS systems and current ISFET-based sequencing approaches.This disclosure is directed to a patentable class ofChemically-sensitive Field-Effect Transistors (ChemFETs) that resolvemany of the current issues associated with chemical and biologicalanalyses, for example, nucleic acid hybridization, NGS sequencing,hybridization detection, genetic diagnostics, genome identification,species identification, nucleic acid capture, genotyping, analytedetection and identification, etc., systems incorporating such ChemFETs,and methods of making and using such ChemFETs.

One aspect of the present disclosure is a ChemFET. These ChemFETs arepreferably fabricated using semiconductor IC fabrication methods on asemiconductor wafer used for semiconductor manufacturing, and inpreferred examples, on top of or over an integrated circuit structuremade using semiconductor IC fabrication methods. The instant ChemFETstypically include a conductive source, a conductive drain, and a channelcomposed of a one-dimensional nanomaterial (1D nanomaterials are verylong in comparison to their cross-sectional area and may be thought ofas wires or tubes, with silicon nanowires (SiNWs) or carbon nanotubes(CNTs) being examples) or a 2D nanomaterial (2D nanomaterials are verythin and spread in two directions to form sheets, with graphene or MoS₂being examples) and/or a three-dimensional (3D) transistor material,which channel extends from the source to the drain and may be fabricatedusing semiconductor IC fabrication techniques on top of or over a waferor other substrate. In some examples there may be multiple channelsbetween the source and the drain. For instance, a substrate, such as asilicon substrate may be provided, upon which a non-conductivedielectric layer, e.g., an oxide layer, may be positioned, within whichor over which the source and drain electrodes may be deposited, and ananomaterial channel member formed there between, which channel membermay additionally be at least partially covered or coated with anothernon-conductive insulation layer, such as an oxide or organic analyte orreaction sensing layer. Specifically, in various examples, anon-conductive, e.g., oxide, layer may be disposed on the channel memberand/or across the channel region.

In some examples, the ChemFET may also include a gate or gate region,e.g., a solution gate, and/or a reference or gate electrode. In otherexamples the ChemFET may include more than one gate, such as a dual gatecomprising, for example, a solution gate and a backgate. In suchexamples the backgate may be configured as a global backgate affectingmultiple ChemFETs or may be a series of local backgates, one for eachChemFET. In another example the gate may partially or even fullysurround a portion of the channel (a so-called Gate All-Around or GAAstructure). Associated circuitry, such as Read-Out Integrated Circuits(ROIC) or a processor, may also be included or otherwise be functionallyassociated with a ChemFET of the disclosure (or array thereof) in orderto process and analyze signals generated thereby.

In use, desired chemical reactions or biologic activity that occurs inproximity to the ChemFET results in a change in electric charge orelectric field strength that can be sensed. Particularly, changes inelectric charge or electric field affect the gate voltage which in turnchanges conductance through the 1D, 2D, and/or 3D channel memberconnecting the source and the drain electrodes—thus chemical reactionsor biologic activity may be transduced and detected by the ChemFET. Forinstance, in some examples, sensing of a desired reaction or biologicactivity produces an alteration, e.g., a shift, in an I-V curve, forexample, an Id-Vg curve, where Id is the drain current and Vg is thegate to source voltage, or a parameter of an I-Vg curve, e.g., thecurve's slope or position relative to the horizontal axis, correspondingto the ChemFET. A processor functionally associated with the ChemFET maybe used to compare a reference I-V curve (or parameter thereof) for awell (or other capture region or structure) and an I-V curve (or thecorresponding parameter thereof) generated in connection with a chemicalreaction or biologic activity occurring in the well (or other captureregion or structure associated with the ChemFET). If the processordetects a difference between the reference and reaction-associatedcurves that exceeds a predetermined threshold, a positive result can beindicated. Likewise, a negative result may be detected in the absence ofsuch an effect.

Another aspect of the present disclosure concerns biosensors based on aChemFET according to the devices, systems, and methods provided herein.Such biosensors may include a structure comprising a substrate and anon-conductive, e.g., oxide, dielectric layer comprising a conductivesource and a conductive drain, a 1D, e.g., Si NW or CNT, or 2D, e.g.,graphene, or 3D channel extending from the source to the drain, andfurther including a well, chamber, passivation opening or otherstructure suitable for analyte capture and analysis associated with anexterior surface of the analyte or reaction sensing insulation layerand/or the channel nanomaterial member. An additional non-conductive,e.g., oxide, passivation layer may be disposed on and/or around thechannel nanomaterial and/or channel region, which passivation layer maybe configured so as to form the well and/or chamber.

The analyte or reaction sensing insulation layer may be included of anoxide, for example, an aluminum oxide, hafnium oxide or a tantalumoxide. In some examples, the analyte or reaction sensing oxide layer maybe a thin layer, such as a layer having a thickness of about 30nanometers (nm), 20 nm, 15 nm, 10 nm, 7 nm, 4 nm, or less. The wellstructure (or other opening in the passivation) defines an openingallowing for direct contact with the channel nanomaterial, e.g., thegraphene channel or direct contact with the analyte or reaction sensinginsulation layer, if one is present. In some examples, sensing theoccurrence of a desired chemical reaction, e.g., sensing the presence ofa target biological compound or reactant thereof, is detectable such asby detecting a change in the conductance through the channelnanomaterial and/or the production of a shift in an I-V curve or an I-Vgcurve corresponding to that change in conductance as determined by theChemFET.

Yet another aspect of the present disclosure is a chemically-sensitivegraphene Field Effect Transistor (gFET). A gFET according to thedisclosure may include a CMOS structure comprising a damascene coppersource, a damascene copper drain, and a graphene channel extending fromthe source to the drain. An analyte or reaction sensing insulationlayer, e.g., an oxide layer, may also be included and disposed on oraround the channel. The analyte or reaction sensing oxide layer may becomposed of an aluminum oxide, a hafnium oxide, or a tantalum oxide. Insome examples, the oxide layer may be a thin layer, such as a layerhaving a thickness of about 30 nanometers (nm), or 20 nm, or 15 nm, or10 nm, or 7 nm, or 4 nm, or less. In particular examples, sensing of adesired chemical reaction, e.g., detection of a target biologicalcompound, produces a shift in an I-V curve or an I_(d)-V_(gs) curvecorresponding to the gFET.

Using Etch Stop Layers when Forming Wells or Passivation Openings

Another aspect of the disclosure relates to methods of making ChemFETs,particularly chemically-sensitive gFETs, of the disclosure. In someexamples, these methods involve well formation on or over a 2Dnanomaterial FET. In various instances, such methods include depositinga protective layer, e.g., an etch stop layer (ESL) or hard mask layer,on or over a channel of a 2D nanomaterial ChemFET device structure.These methods may include etching through a passivation layer and aportion of the ESL with a first etching method to create at least a wellor opening in the passivation formed over a channel region that mayinclude a channel nanomaterial configured to form a channel.

These methods may also include a second etching of the remainingprotective ESL or hard mask layer over the channel to expose the channelnanomaterial or an analyte or reaction sensing layer over the channelnanomaterial within the formed well or opening in the passivation. Invarious examples, the protective passivation layer may be included of aninorganic material, for example, an oxide, a nitride, a carbide, anoxy-nitride, a carbon-doped oxide, or a fluorine-doped oxide material.In other examples, the protective passivation layer may be composed ofan organic material, such as a polymer comprising polyimide or PBO. Inyet other examples, the protective passivation layer is composed of bothinorganic and organic materials.

Passivation Well or Opening Manufacturing Method

Other aspects of the disclosure concern methods for manufacturing apassivation well formation or opening for a 1D, 2D, and/or 3Dnanomaterial ChemFET with an organic protective passivation layer. Suchmethods may include depositing an organic protective passivation layerover and/or on a channel of a 1D, 2D, and/or 3D nanomaterial FET of asemiconductor device structure. The methods may also includelithographic patterning of the organic protective passivation layer tocreate one or more well formation or passivation opening locations overthe channel. The method may further include removing the protectivelayer over the channel to expose the channel within the well formationor passivation opening.

Method to Form a Gate All-Around Structure

In a related manufacturing aspect, the methods of the disclosure includedepositing a 1D or a 2D nanomaterial, for example, graphene, or 3Dnanomaterial, to form a channel on an exposed conductive, e.g., metal,layer of an integrated circuit structure. The integrated circuitstructure may include a semiconductor substrate, a dielectric layerand/or non-conductive layer, and the conductive, e.g., metal orelectrode, layer. These methods may include utilizing a patternedmaterial to expose a portion of a channel area and one or more adjacentareas.

These methods may also include etching the dielectric material, e.g.,starting with the adjacent areas, thereby exposing a trench under thechannel, and exposing the metal in the channel area. Such methods mayfurther include etching the metal from underneath and/or around thechannel, e.g., graphene, material to create a ChemFET with a GAAstructure.

Methods to Prepare a Growth Substrate

Another aspect of the disclosure relates to methods for preparing agrowth substrate that are useful to produce the ChemFET channelnanomaterials, particularly graphene chemically-sensitive gFET channelnanomaterials, of the disclosure. These methods may include depositing ametal catalyst layer, e.g., Ni, Ru, Cu or Pt, on a substrate and/or anon-conductive layer thereof, and annealing the metal catalyst, whereinthe annealing may occur in an environment that includes hydrogen, suchthat the resulting metal catalyst layer is a predominantly singlecrystalline metal catalyst layer with a crystal orientation. Suchmethods may include activating the metal catalyst layer, such as by aplasma method, which may include a hydrogen gas and/or anitrogen-containing gas.

Detection and Sequencing of Nucleic Acids

The detection and sequencing of nucleic acids, such as deoxyribonucleicacid (DNA) or ribonucleic acid (RNA), is a fundamental part ofbiological discovery. Detection and/or sequencing are useful for avariety of purposes, and are often used in scientific research, drugdiscovery, medical diagnostics, and in the prevention, monitoring, andtreatment of disease. For instance, the genomics and bioinformaticsfields, which rely on nucleic acid detection and sequencing techniques,are concerned with the application of information technology andcomputer science to the field of molecular biology. In particular,bioinformatics techniques can be applied to process and analyze variousgenomic data, such as from an individual so as to determine qualitativeand quantitative information about that data that can then be used byvarious practitioners in the development of diagnostic, prophylactic,and/or therapeutic methods and products for detecting, preventing,treating, or at least ameliorating disease states, thus improving thesafety, quality, and effectiveness of health care. The need for suchdiagnostic, therapeutic, and prophylactic advancements has led to a highdemand for low-cost nucleic acid detection and sequencing methods,devices, and reagents, which in turn have driven, for example, thedevelopment of high-throughput sequencing, termed as Next GenerationSequencing (NGS).

Generally, the approach to DNA and/or RNA analysis, such as for geneticdiagnostics and/or sequencing, involves nucleic acid hybridization anddetection. For example, various conventional hybridization and detectionapproaches include the following steps. For genetic analysis, an RNA orDNA sample obtained from a subject to be analyzed is isolated andimmobilized on a substrate. A detectable probe of a known geneticsequence, e.g., having a nucleotide sequence that corresponds to adisease marker (e.g., a marker evidencing a bacterial, fungal, or viralinfection, a single nucleotide polymorphism (SNP) associated with aparticular disease such as cancer, an autoimmune disease, etc.) is thenadded to the substrate, typically in a reaction mixture containing therequisite reagents to allow the probe to interact with its target, ifpresent in the sample. If the disease marker is present, a bindingevent, e.g., hybridization, will occur and because the probe isdetectable (e.g., via the inclusion in the probe of a detectable labelsuch as a fluorescent dye if the detection scheme is optically-based),the hybridization event can either be or not be detected, therebyindicating the presence or absence of the disease marker in thesubject's sample.

For DNA/RNA sequencing and/or detection, first, an unknown nucleic acidsequence to be identified, e.g., a single-stranded sequence of DNA/RNAfrom a subject, is isolated, amplified, and immobilized on a substrate.Next, in the presence of a primer complementary to a portion of theisolated nucleic acid sequence to be sequenced and/or identified,(preferably labeled) nucleotides, and a suitable DNA polymerase, anucleic acid sequencing and/or detection reaction may take place. Insuch an instance, where the primer recognizes a corresponding sequenceof the isolated and/or bound nucleic acid sequence, the polymerase canbegin to add one or more labeled nucleotides to extend the primer in thepresence of the unknown nucleic acid sequence, using the unknown nucleicacid sequence as the template. When the primer is extended, the mostrecently added labeled nucleotide, which hybridizes via hydrogen-bondingto its complementary base in the unknown sequence immobilized on thesurface of the substrate, the most recent nucleotide's addition can thenbe detected, e.g., optically, or electrically. These steps are thenrepeated until the entire DNA/RNA molecule has been completelysequenced. Typically, these steps are performed on a Next Gen Sequencerwherein thousands to millions of DNA fragments can be sequencedconcurrently in the NGS process.

As will be appreciated, a central challenge in DNA sequencing based onthe sequencing of numerous short DNA fragments is assembling full-lengthgenomic sequences, e.g., chromosomal sequences, from a sample of geneticmaterial, as the sequencing methods used in NGS processes do not producefull-length gene or chromosomal sequences from the sample DNA that canthen be used for a desired genetic analysis, assessment of geneticvariation or identity between the subject's sample and a reference gene,genome, etc. Rather, sequence fragments, typically from 100-1,000nucleotides in length, are produced without any indication as to wherein the genome they reside. Therefore, in order to generate full-lengthgene or chromosomal genomic constructs or determine variants withrespect to a reference genomic sequence, such DNA sequence fragmentsneed to be mapped, aligned, merged, and/or compared to a referencegenomic sequence. This is true also for SNP genotyping, even though inthat case a full-length gene or chromosomal sequence need not beconstructed, but at least a length of base pairs that encompasses theloci of the SNP must be constructed, e.g., lengths of 250 base pairs,150 base pairs, or even 50 base pairs may be sufficient for SNPidentification. Through such processes the variants of the samplegenomic sequences from the reference genomic sequences may be determinedby suitable bioinformatics approaches, such as by implementing asuitable variant calling application.

Even so, as the human genome includes approximately 3.1 billion basepairs, and as each sequence fragment in an NGS process is typically onlyfrom 100 to 500 to 1,000 nucleotides in length, the time and effort thatgoes into building full-length genomic sequences and determining thegenetic variants therein is quite extensive, often requiring the use ofseveral different computer resources applying several differentalgorithms over prolonged periods of time. This is because in a givenNGS analysis, thousands, millions, or even billions of DNA sequences aregenerated, which sequences must then be aligned and merged in order toconstruct a genomic sequence that approximates a chromosome or genome insize. A step in this process often includes comparing the DNA fragmentsequences to a reference sequence to determine where in the genome thefragments reside.

In order to perform an NGS analysis, genetic material from a subjectmust be pre-processed. This preprocessing may be done manually or via anautomated preparation system. Typically, preprocessing involvesobtaining a biological sample from a subject, such as throughvenipuncture (blood, plasma, serum), buccal swab, urine, saliva, etc.,and treating the sample to isolate the DNA therefrom. Once isolated, theDNA is then fragmented and denatured.

The DNA (or portions thereof) may then be amplified, e.g., viapolymerase chain reaction (PCR), so as to build a library of replicatedstrands that are now ready to be sequenced, such as by an automatedsequencer. The sequencing machine is configured to sequence theamplified DNA strands, e.g., by synthesis of new, complementary strandsthat include labeled nucleotides, from which the nucleotide sequencesthat make up the DNA in the sample can be determined.

Further, in various instances, such as in building the library ofamplified strands, it may be useful to provide for over-coverage orover-representation when preprocessing a given portion of the DNA Toprovide this over-representation, increased sample preparation may berequired, thus making the process more expensive, although such stepsoften yield an enhanced probability of the end result being moreaccurate.

Once a library of amplified DNA strands has been generated, the strandsmay be injected into an automated sequencer that can then determine thenucleotide sequences of the strands, such as by synthesis. For instance,amplified single-stranded DNA can be attached to a nano- or microbeadand inserted into a test vessel, e.g., an array. All the necessarycomponents for synthesis of its complementary strand, including labelednucleotides (for adenine (A), cytosine (C), guanine (G), and thymine(T)), are also added to the vessel but in a sequential fashion. In someinstances, one or more the nucleotides, e.g., “A”, “C”, “G”, and “T's”that are added may be configured so as to be reversible terminators,e.g., such that once incorporated into a growing strand beingsynthesized cause the synthesis reaction for that particular strand tobe terminated at that point of incorporation, thereby producing severalstrands of terminated sequences that collectively represent the entiretemplate nucleic acid sequence. Hence, in performing a nucleic acidsynthesis or detection reaction all of the necessary nucleotidereactants are added, either one at a time or all together, to see whichof the nucleotides is used to extend a primer molecule.

Particularly for an optically-based NGS system, after each addition,unincorporated nucleotides are washed away and a light, e.g., a laser,is then shone on the array. If the label fluoresces, that fluorescencecan be detected, thereby indicating which nucleotide has been added and,due to the nature of the genetic code, which complementary nucleotidewas present in the template DNA fragment in the subject location. Inprocesses where labeled nucleotides are added one at a time, ifextension occurs, then its indicative fluorescence will be observed. Ifextension does not occur, the test vessel may be washed and theprocedure repeated until the appropriate one of the four nucleotidesbinds to its complement and is incorporated by the polymerase into thegrowing DNA strand at the subject location such that its indicativefluorescence of its label can be detected.

Where all four reversible terminator nucleotides are added at the sametime, each may be labeled with a different fluorescent indicator; whenthe complementary labeled nucleotide binds to its complement in thetemplate DNA strand such that it is then added by the polymerase duringthe elongation step, the identity of the added, labeled nucleotide atthe subject position can then be determined, such as by the color of itslabel's fluorescence. As will be appreciated, the use of all fourlabeled nucleotides in a given reaction greatly accelerates thesynthesis process.

After each elongation reaction, the complex is then washed and thesynthesis steps are repeated for the next position. This process ofelongation and detection is then repeated for all nucleotides for asmany positions as are present in the input DNA fragments or for so longas the sequencing machine directs (e.g., 100, 500, 1,000, or morecycles), thereby generating “sequence reads” of the over-sampled nucleicacid segments. The resulting sequence data is collected.

Usually, a typical length of a sequence replicated in this manner isfrom about 100 to about 500 or about 1000 base pairs, such as between150 to about 400 base pairs, including from about 200 to about 350 basepairs, such as about 250 base pairs to about 300 base pairs dependent onthe sequencing protocol being employed. Further, the length of thesesegments may be predetermined, e.g., engineered, to accord with anyparticular sequencing machinery and/or protocol by which it is run. Inany event, the end result is a readout, or “read”, that is included ofan extended DNA fragment synthesized from an input DNA fragment.

Extended DNA fragments typically range from about 100 to about 1,000nucleotides in length, and each nucleotide is labeled in such a mannerthat every nucleotide in the sequence can be identified because of itslabel. Hence, since the human genome is included of about 3.1 billionbase pairs, and various known sequencing protocols usually result inlabeled replicated sequences, e.g., reads, from about 100 or 101 basesto about 250 or about 300 or about 400 bases, the total number ofsegments that need to be sequenced, and consequently the total number ofreads generated for single read coverage can be anywhere from about10,000,000 to about 40,000,000, such as about 15,000,000 to about30,000,000, dependent on how long the label replicated sequences are.

Therefore, the sequencer may typically generate about 30,000,000 reads,such as where the read length is 100 nucleotides in length, so as tocover the genome once. However, to ensure the accuracy of a particularbase call (e.g., A, C, G, or T) at a particular nucleotide position, itis desirable that copies of each fragment in a sample be sequenced 5,10, 20, 30, or more times, in some cases up to 500 or more times. Suchover-sampling thus results in even more reads, thereby requiring moreanalysis. Fragment amplification in the pre-processing phase helps tofacilitate such redundancy.

However, in part, due to the need for the use of optically detectable,e.g., fluorescent, labels in the sequencing reactions being performed,the required instrumentation for performing such high throughputsequencing is bulky, costly, relatively slow, and not portable.

For this reason, a number of new approaches for direct, label-free DNAsequencing have been proposed. For instance, among the new approachesare detection methods that are based on the use of various electronicanalytic devices. Such direct electronic detection methods have severaladvantages over the conventional NGS platform. For example, the detectormay be incorporated in or on the substrate of a semiconductor IntegratedCircuit (IC) chip itself, such as employing a biosystem-on-a-chipdevice, such as a Complementary Metal Oxide Semiconductor (“CMOS”) ICdevice.

More particularly, in using a semiconductor IC device in geneticdetection, the output signal representative of a nucleotide's additionin a DNA sequencing reaction can be directly acquired and processed onan IC chip. In such an instance, automatic recognition is achievable inreal time and at a lower cost than is currently achievable usingconventional NGS processes and equipment. Moreover, due to the maturityand high integration available with semiconductor IC devices, such asCMOS devices, they may be employed for such electronic detection, makingthe process simple, fast, inexpensive, and portable.

Particularly, in order for NGS methods to become widely used fordiagnostic and therapeutic applications in the healthcare industry,sequencing instrumentation will need to be mass produced with a highdegree of quality and economy. One way to achieve this is to recast DNAsequencing in a format that fully leverages the manufacturing basecreated for IC chips, such as CMOS chip fabrication, which is thecurrent pinnacle of high technology large scale, high quality, low-costmanufacturing. To achieve this, ideally, the entire sensory apparatus ofthe sequencing device should be embodied in a semiconductor IC chip,manufactured in the same fabrication (“Fab”) facilities used for logicand memory chips. Recently, such a sequencing IC chip, and theassociated sequencing platform, has been developed and commercialized byIon Torrent, a division of Thermo-Fisher, Inc. The promise of this ideahas not been realized commercially, however, due to the fundamentallimits of applying a Metal Oxide Semiconductor Field Effect Transistor,or MOSFET, included of a typical semiconductor, such as silicon, as abiosensor. In particular, when a MOSFET is coupled to an ion-sensitivesensing plate used in solution as a biosensor, it is referred to as anISFET (Ion Sensitive Field Effect Transistor). Particular limitations ofISFET devices include a lack of sensor sensitivity and poorsignal-to-noise characteristics as the semiconductor node scales down tolower geometries of the transistor (channel and gate length).

FIG. 1A illustrates an example of one type of ISFET with a traditionalsemiconductor FET as the sensing transistor (FET). The illustrated ISFET(200) has a semiconductor base (10), e.g., a silicon wafer, within andupon which are formed semiconductor FETs. The semiconductor FETs areincluded of a source (202), drain (204), gate (208) and gate dielectric(210). The source (202) and drain (204) of a traditional semiconductorFET are formed by regions of implanted and diffused species (e.g.,boron, arsenic, or phosphorous ions) that alter the number of carriers(holes or electrons) within those regions, so for example n-type sourceand drain regions may be created by implanting and diffusion of arsenicions in a p-type semiconductor substrate. Contacts, e.g., silicide, areformed to the source and drain diffusions, such as a source contact(212) and a drain contact (214), and metal interconnects (25) couplewith the contacts and are used to connect to and between the pluralityof transistors. The metal interconnects (25) are embedded in adielectric layer (20).

When an appropriate gate voltage is applied to the gate (208), suchvoltage being referenced to another component of the transistor, such asthe source (202), the FET “turns on” and carriers will flow between thesource (202) and the drain (204). The voltage required to tum on the FETis call the threshold voltage. When the traditional semiconductor FET isturned on the flow of carriers defines a channel region (206). Note thatthis channel region (206) refers to a location of charge carriers withinthe semiconductor. In this example, there is no flow of carriersdefining the channel region (206) when the traditional semiconductor FETis turned off. An electrical characteristic of a FET, such as currentflowing between the source (202) and the drain (204), may be modified bychanges in the gate voltage—and this forms the basis for using a FET asa sensor, i.e., if the target, analyte or reaction to be detectedcreates a change in electric field or charge density which in tumchanges the gate voltage—then this may be detected by a change inmonitored electrical characteristic of the FET such as drain current.

In the case of an ISFET (200) fabricated from traditional semiconductorFETs there must be a way to communicate the sensed electric field orcharge density of the target reaction or analyte to the FET transistor.As depicted in FIG. 1, an ISFET (200) may include a sensing plate (216),typically a metal plate, that is connected by interconnects (25) to thesensor transistor gate (208). This sensing plate is in communicationwith or is proximate to region, such as a chamber (37) where the analyteor reaction to be detected will be present. The chamber (37) is part ofa well structure (38) formed from insulating passivation material (35).The chamber (37) has sidewalls (39).

An ISFET relies on a fluid (64) that covers the sensing area and fillsthe chamber (37) to provide a minimum gate voltage to turn on the sensortransistor. The gate voltage is applied by a reference electrode (66)coupled to the fluid or solution—creating a solution gated FET. In someinstances, an analyte or reaction-sensitive layer (218) is formed overthe sensing plate (216). The ISFET (200) is typically replicated manytimes on a semiconductor IC chip to form an array of ISFET sensor cellsthat include a sensor IC chip. In order to read a signal from just oneof the ISFETs at one time from the array of ISFETs on the IC chip anaccess transistor, one for each ISFET, is used to control access to theselected ISFET to be read.

Thus, for an ISFET based on traditional semiconductor FETs, there aretwo transistors (the sensor transistor and the access transistor)required for each sensing location. The need for two semiconductortransistors per sensor has implication on the size of those transistors(i.e., the transistors for a cell defined by two transistors willnecessarily have smaller transistors than a cell defined by onesemiconductor transistor). Smaller transistors create more noise thanlarger transistors.

Another consideration is that more semiconductor transistors (e.g., 2per cell versus 1 per cell) require more interconnect connections andwill lead to the need for more levels of interconnect wiring toaccomplish connecting to all the transistors. Increases in the number oflevels of interconnect wiring and increases in the interconnect lengthhave deleterious effects on the noise of the ISFET sensor. As thisdiscussion has highlighted, the noise of an ISFET made from atraditional semiconductor FET may be higher than other FETs used forsensing. Noise in a sensor is important since the detection signal mustbe discriminated separately from the noise in the sensor. The higher thesignal to noise ratio then the better the sensitivity of the sensor willbe.

As is known, a Field Effect Transistor (FET) manufactured by typicalsemiconductor IC fabrication processes includes a gate over a channelregion, a channel region formed by charge carriers in the semiconductormaterial connecting source and drain regions when an appropriate gatevoltage is applied, and an insulating barrier separating the gate fromthe channel. The operation of a conventional FET relies on the controlof the channel's conductivity, and thus the drain current, by a voltage,designated VGS, applied between the gate and source. For high-speedapplications, and for the purposes of increasing sensor sensitivity,FETs should respond quickly to variations in VGS. However, this requiresshort channel lengths and fast carriers in the semiconductor channel.

Furthermore, for a sensor chip to be used for DNA sequencing, requiringon the order of 30,000,000 reads as described above, the size of theindividual sensors in the sensor array must be made small enough to fitmillions of sensors on the chip. In this case there are physicallimitations to the chip size due to the photolithography systemsavailable for wafer and chip manufacturing (e.g., a maximum chip size onthe order of 25 mm square) which in turn limit the size of the sensorson the chip given the large number of sensors needed in the array.

Another consideration is that an ISFET used for DNA sequencing isarranged as an array of sensors—each of which must be individuallyaddressable to read the signal of any DNA hybridization that isoccurring local to that sensor. To achieve both this individual sensorcell addressability as well as sensing function the sensor cell requiresat least two CMOS (or other semiconductor) transistors—one to controlthe access to the cell for reading and the other as the sensortransistor to transduce the DNA binding or hybridization event into anelectrical signal. Because of this need for a minimum of two CMOStransistors per sensor cell the transistors must be even smaller, e.g.,at least 2 times smaller, than what would be required due to theaforementioned geometrical constraints derived from the maximum chipsize and number of sensors in the array. This further constraint on thesize of the CMOS transistor used for sensing directly relates to thechannel length of that transistor.

Unfortunately, FETs with short channel lengths frequently suffer fromdegraded electrostatics and other problems (collectively known as shortchannel effects), such as threshold-voltage roll-off, drain-inducedbarrier lowering, and impaired drain-current saturation, which result ina decrease in sensor sensitivity. Nevertheless, scaling theory predictsthat a FET with a thin barrier and a thin gate-controlled region(measured in the vertical direction) should be robust againstshort-channel effects down to very short channel lengths (measured inthe horizontal direction).

Accordingly, the possibility of having channels that have high surfacearea to volume ratio (e.g., are very thin in the vertical dimension likea 2D nanomaterial or have a small cross-section area like a 1Dnanomaterial) yet still allow for high-speed transmission of carrierswould allow for increased sensor sensitivity and accuracy. What isneeded, therefore, is a FET device that is configured in such a mannerand includes such materials that in combination of structure andmaterials it offers a FET sensitivity that is higher than is currentlyachievable in present FET applications. A solution that includes such aFET device designed for use in biological applications, such as fornucleic acid detection, sequencing, and/or other diagnosticapplications, would be especially beneficial.

ChemFET and ChemFET Sensor Array Overview

Provided herein are devices, systems, and methods of employing the samefor the performance of genomics, bioinformatics, analyte or biologicreaction detection or analysis. The devices, systems, and methods of thedisclosure are directed in part to Chemically-sensitive Field EffectTransistor (ChemFET) sensors, integrated circuits, and arrays employingthe same for analyte detections and measurements. The present ChemFETsensors, arrays, and integrated circuits may be fabricated usingconventional semiconductor processing techniques, e.g., CMOS techniques,based on improved ChemFET sensor and array designs that increasemeasurement sensitivity and accuracy, and at the same time facilitatesignificantly small sensor sizes and dense 1D, 2D, or 3D, e.g., gFET,sensor-based arrays. Particularly, improved fabrication techniques, aswell as improved sensor devices, and their use, employing onedimensional (1D) or two-dimensional (2D) nanomaterial channel layersand/or having a three-dimensional (3D) structured layer incorporatedtherein, provide for rapid data acquisition from small sensors to largesensors, including dense arrays of sensors.

Such arrays may be fabricated, as described herein, and employed todetect the presence of an analyte, changes in analyte concentration,biologic activity and/or the identity of various analyte types in a widevariety of chemical and/or biological processes, including DNAhybridization and/or sequencing reactions. More particularly, presentedherein are ChemFET based sensor arrays that have been configured tofacilitate DNA hybridization and sequencing techniques, as well as theresultant detection of the same, which take place proximate a sensingzone that has been adapted to include or otherwise be proximate to a 1Dor 2D or 3D nanomaterial channel element. Specifically, in variousexamples, ChemFET devices are provided, where the devices include one ormore, e.g., a plurality, of sensing zones that have been adapted to havea 1D or 2D nanomaterial channel associated therewith so as to decreasesensor length and/or increase sensor width at the same time asincreasing sensor sensitivity. Further, in various instances, a 3Dstructural layer may be included, such as to extend the verticaldimension of the sensing zone. In such instances, the devices mayinclude one or a number of sensing zones that have been configured toreceive a fluid or solution containing one or more reactants, whereinwhen conditions are such to favor a reaction, the result thereof isdetectable by the ChemFET.

Accordingly, presented herein are improved biochemical sensor devicesthat are configured for detecting changes in or near to a channel regionand/or solution that result from the occurrence of a reaction betweentwo reactants or biologic activity proximate a sensing zone of thedevice, such as within the channel region. In particular instances, thedetectable changes may be based on monitoring fluctuations in an ion,e.g., hydrogen ion, concentration (pH), variations in analyteconcentration, biologic activity and/or reactions associated withchemical processes relating to DNA synthesis or hybridization,biomolecule detection, analyte detection or cell monitoring, such aswithin a sensing chamber of a 1D or 2D or 3D based biosensor chip.

Specifically, the present disclosure is at least in part directed to aChemFET for analysis of biological or chemical analytes or reactions orbiologic activity that solves many of the current problems associatedwith nucleic acid sequencing and genetic diagnostics as well as analytedetection. Methods of fabricating such devices as well as their use inthe detection of biochemical reactions or analytes are also provided.

Other types of ChemFETs contemplated by the present disclosure includeenzyme FETs (EnFETs) which employ enzymes to detect analytes, SchottkyBarrier FETs, Tunneling FETs and Junctionless FETs, in addition toMOSFETs or ISFETs. It should be appreciated, however, that the presentdisclosure is not limited to ISFETs and EnFETs, but more generallyrelates to any FET, such as Schottky Barrier FETs, Tunneling FETs andJunctionless FETs, that is configured for some type of chemicalsensitivity.

As used herein, chemical sensitivity broadly encompasses sensitivity toany molecule of interest, including without limitation organic,inorganic, naturally occurring, non-naturally occurring, chemical andbiological compounds, such as ions, small molecules, polymers such asnucleic acids, proteins, peptides, polysaccharides, or reactions orbiologic activity related to those molecules and compounds and the like.

Generally, a ChemFET device will include a conductive source and aconductive drain in or on a dielectric material, a channel extendingbetween the source and drain, e.g., included of a 1D or 2D nanomaterial,that functions as a sensing layer, an insulating passivation layer withan opening or well on or over the channel and a gate to control theconductance of the channel. In some examples the ChemFET may alsoinclude an analyte or reaction sensitive material layer over or on thenanomaterial channel.

In various instances, the structures may further include or befunctionally connected to an ROIC, or a processor, such as forprocessing generated data, e.g., sensor-derived data. Accordingly, thestructures may be configured as, or otherwise include, an integratedcircuit, and/or may be an ASIC, a structured ASIC, a processor, or anFPGA or include analog to digital converters, row and column addressingcircuitry, amplifying, or filtering or other readout circuits. Inparticular instances, the structures may be configured as asemiconductor IC, such as a Complementary Metal-Oxide Semiconductor(CMOS) IC, which in turn may be configured to include a ChemFET, e.g., agFET, containing one or more of a conductive source, a conductive drain,a gate, which may be a solution gate, and/or a channel. For instance,the sensor array IC chip may include a CMOS configuration having anintegrated circuit that is fabricated on a silicon wafer, which mayfurther be adapted to include a nanomaterial-based ChemFET.

ChemFET Primary Base and Dielectric Layer Structure

For instance, in one aspect of the present disclosure, achemically-sensitive transistor, such as a ChemFET that is fabricated ona primary base structure, such as a wafer, e.g., a silicon wafer, isprovided. The primary base structure may include diffusions or dopedareas to define source and drain regions used to create typicalsemiconductor transistors (11) (e.g., CMOS transistors). Thesetransistors may be useful for creating circuits for interfacing with thechemically sensitive transistors (ChemFETs)—but they are separate fromthe chemically-sensitive transistors (ChemFETs). In various instances,the primary base structure may include one or more additionalstructures, for instance, in a stacked configuration, such as includingat least a dielectric material layer. For example, the primary basestructure may include a secondary structure, such as composed of adielectric material, which may be included on top of, over, or otherwisebe associated with, the primary base structure, and may form adielectric layer. Particularly, the secondary dielectric layer may be aninorganic material layer, such as including a silicon oxide, e.g., asilicon dioxide, or a silicon nitride or a silicon carbide or mixturesof these materials, or an organic material, such as a polyimide, BCB,PBO or other like material.

ChemFET Source and Drain

The secondary structure and/or dielectric layer may include a furtherstructure containing one or more of a conductive source and/or aconductive drain, such as separated one from another by a space, andembedded in the secondary structure materials and/or may be planar ornon-planar with a top surface of the dielectric. In such an instance,the dielectric layer may include the ChemFET conductive source and drainsuch as where the source and drain are composed of a conductor, such asmetal or polysilicon, such as a damascene copper source and a damascenecopper drain. Other metals such as tungsten, aluminum, platinum,titanium, or gold could also be used as the conductive source and drain.In other instances, such as for a semiconductor NW, e.g., a Si NW,portions of the NW itself may be doped to form conductive sources ordrains and these in turn may be contacted by a metal or polysiliconconductive material.

The conductive source and drain may contact the channel at the bottom ofthe channel nanomaterial, at the top of the channel nanomaterial or fromboth the top and the bottom of the channel nanomaterial. In otherinstances, holes or trenches may be formed in the channel nanomaterialand conductive source or drain material may be deposited in those holesor channels so that not only is a surface of the channel nanomaterialcontacted but also one or more edges of the nanomaterial, defined by theholes or trenches, are contacted.

In other examples the conductive source and drain material, or anintermediary material between the conductive source or drain and thechannel nanomaterial is chosen so that the work function of thosematerials more closely matches the work function of the channelnanomaterial.

In various instances the dielectric layer may further include structuressuch as interconnects that are used to connect to the semiconductortransistors or to the conductive sources and conductive drains of theChemFETs or the dielectric layer may include contacts that contactdiffusion regions that define sources and drains for the semiconductortransistors (e.g., CMOS).

ChemFET Channel

In various instances, one or more of the structures having the metallayers therein may include a surface, e.g., a side and/or top surface,which surface(s) may include or incorporate a ChemFET channel, such aswhere the surface and/or channel may be configured to extend from theconductive source to the conductive drain. The ChemFET channels arephysical structures formed of 1D or 2D nanomaterials. The ChemFETchannels contrast with the channels of a typical semiconductortransistor which are formed in the semiconductor material between thesource and drain diffusion regions only when a sufficient gate voltageis applied greater than the transistor threshold voltage. An exemplarylength of the surface and/or channel from the source to the drain of aChemFET may range from about 0.001 microns to about 10 microns, such asfrom about 0.01 microns to about 5 microns, for instance, from about0.05 micron to 3 microns, including about 0.1 or about 0.5 microns toabout 1 or about 1.5 or about 2 microns. Note that in some cases it maybe desirable to fabricate a ChemFET with substantially longer channellength—even up to several millimeters in length. An exemplary width ofthe surface and/or channel from side to side may range from about 0.001microns to about 10 microns, such as from about 0.01 microns to about 5microns, for instance, from about 0.05 microns to 3 microns, includingabout 0.1 or 0.5 microns to about 1 or about 1.5 or about 2 microns.

In some instances, there may be multiple ChemFET channels formed betweenone source and one drain. This may particularly be true for channelsincluded of 1D nanomaterials such as Si NWs or CNTs. When multiplechannels are formed between a source and a drain the channels may bealigned with each other (ordered), e.g., parallel to each other, or theymay not be aligned with each other (unordered). Multiple channels may bearranged in either a horizontal plane, a vertical plane, or as an arrayof channels arranged in 3D space both horizontally and vertically.

ChemFET Channel Transconductance

Particularly, in various instances, it may be useful to maximize channeltransconductance, such as by decreasing the channel length and/orincreasing channel width and/or dimensionality, so as to increase thesensitivity of the sensors, such as in a sensor array. For instance, toachieve enhanced transistor transconductance, the channel may beconfigured so as to include a short channel length, e.g., as short alength as possible, while at the same time including a larger channelwidth, e.g., as large as width as possible, within the sensor array, ina manner adapted for keeping the overall dimensions of the array ascompact as possible. For example, the equation for transconductance of afield effect transistor, such as for a transistor presented herein, is:g_(m) ∝ μC_(ov) W/L V_(sd); where gm is the transconductance, μ is thecarrier mobility, C_(ov) is the overall capacitance of the oxide orother layers over the transistor channel, W is the channel width, L isthe channel length, and V_(sd) is the voltage from the source to thedrain. Since gm directly relates to the sensitivity of the sensor it maybe desirable to increase gm through moderating the terms shown in theequation.

In particular increasing the W/L ratio (maximizing W and minimizing L)will increase gm. In particular instances, a useful length of thechannel from the source to the drain ranges is less than 1 micron, suchas less than 500 nm, such as less than 50 nm, and may be as short as thefabrication process will allow without generating defects or resultsthat render the device unusable. A particularly useful channel lengthmay be 20 nm or less.

Conversely, the width of the channel may be as wide as possible. In suchinstances, the width of the channel is not governed by the fabricationprocess as much as by the design requirements of the overall sensorchip. In various instances, hundreds of thousands to many millions ofsensors may be positioned on the sensor chip. With this large number ofsensors, the individual sensor size and pitch (e.g., which may directlyaffect the channel width) may be kept small, such as reasonably small,so as to prevent the chip from being so large as to be unable to befabricated (e.g., exceeds the photolithography reticle size) or tooexpensive (due to the effect of defect density on a large chip size). Apractical range of channel width in particular instances may be from 0.1micron to 2 microns, e.g., for a simple rectangular channel design. Insome cases, it may be desirable to increase the channel length tochannel width ratio through the use of design techniques—for example,structured and/or an interdigitated 2D or 3D tooth and comb designs canprovide for short channel lengths and large channel widths within arelatively compact area. In some instances, there may be multiplealternating layers of dielectric material and channel nanomaterial,which can significantly increase the W/L ratio of the channel therebyincreasing the transconductance and ultimately the sensitivity of thedevice.

In other instances, the ChemFET channel transconductance may be improvedby applying a material or process that can help to repair or improvegrain boundaries, wrinkles or other transconductance-limiting artifactsor defects in the channel nanomaterial layer. For example, tin atoms maypreferentially deposit at grain boundaries or defect areas on grapheneand in so doing they will “stitch” across the grain boundaries ordefects allowing charge carriers (holes or electrons) to move morefreely and with higher mobility. An improvement in mobility directlyimproves channel transconductance and ultimately sensor sensitivity.

In other instances, an isolation layer may be applied between thechannel nanomaterial and the dielectric layer. Often the dielectriclayer on a silicon semiconductor chip is a silicon oxide. Silicon oxideis known to trap charges which impedes the mobility of the carriers inthe channel and which also contributes to transistor noise. An isolationlayer, such as a charge trap screening layer, may be formed between theChemFET channel and the dielectric layer. In some instances, thismaterial may be an organic material such as parylene, HMDS or aSelf-Assembling Monolayer (SAM) and In other instances, this materialmay be an inorganic material such as aluminum oxide or preferentiallyhexagonal boron nitride (hBN).

ChemFET Channel Nanomaterial

In certain instances, the ChemFET channel may include a one-dimensionaltransistor nanomaterial, a two-dimensional transistor nanomaterial, athree-dimensional transistor nanomaterial, and/or the like. In variousinstances, a one-dimensional (1D) transistor nanomaterial may beincluded, which 1D nanomaterial may be composed of, for example, acarbon nanotube (CNT) or a semiconductor nanowire, such as a siliconnanowire (Si NW). In various instances, a two-dimensional (2D)transistor material may be included, which 2D nanomaterial may becomposed of a graphene layer, silicene, molybdenum disulfide, blackphosphorous (phosphorene), borophene, tungsten disulfide, boron nitride,tungsten diselenide, stanene, germanane, nickel HITP, and/or metaldichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2,Ti3CN, Nb4C3, or Ta4C3. In particular instances, a three-dimensional(3D) structural material, such as proximate a sensing zone and/orchannel layer may be provided. In various examples, the channel may besituated on, over, under or sandwiched between dielectric layers. Inparticular examples, the channel may include a graphene layer.

ChemFET Analyte or Reaction-Sensitive Layer

Additionally, in various instances, a reaction or analyte orreaction-sensitive layer such as an ion sensitive layer, e.g., aninorganic or organic material layer, may be disposed on or over thesurface and/or channel, such as layered or otherwise deposited on the1D, 2D, e.g., graphene, or 3D layer, and/or an included dielectriclayer. Such an inorganic may be an oxide layer or a nitride layer may bean aluminum oxide, tantalum oxide, titanium oxide, hafnium dioxide,hafnium silicate, zirconium silicate, zirconium dioxide, lanthanumoxide, iron oxide, yttrium oxide or a silicon oxide, such as silicondioxide. Generally, an oxide with high intrinsic buffer capacity ispreferred.

In some instances, it may be advantageous to stack two or more differentinorganic reaction-sensitive layer on top of each other to form anoverall reaction-sensitive layer. In some examples, the oxide layer mayhave a thickness of about 150 nanometers, such as about 100 nanometers,such as about 50 nanometers, such as about 20 nanometers or less, suchas about 15 nanometers, such as 10 or 9 or 7 or 5 nanometers or less. Itmay be advantageous to minimize the thickness of this oxide layer inorder to increase the Cov term in the aforementioned formula for gm thusmaximizing gm.

Many 1D and 2D nanomaterials are relatively difficult to coat with areaction-sensitive inorganic material and in these instances thenanomaterial may be pretreated or activated so that thereaction-sensitive layer will adhere or stick to it. Pretreatment oractivation may include ozone plasma, PVD metal deposition and oxidationof that metal, a sol gel layer, fluoridation, chlorination, oxidation,hydrolysis, or other techniques. After the pretreatment or activation,the reaction-sensitive material may be applied by PVD, CVD, ALD or otherprocesses.

In some instances, an organic material layer may be used as areaction-sensitive layer such as an ion sensitive layer. An organicreaction-sensitive layer ideally will be one that easily adheres orbonds to the underlying nanomaterial layer. In the case of 2Dnanomaterial channels with chemical ring structures, such as graphene, agood choice for an organic reaction-sensitive material is a materialwith a ring structure and that includes functional groups such as OH orO—the ring structure of the reaction-sensitive material may align withthe ring structure of the 2D nanomaterial and allow so-called Pi-Pibonding of the two materials. Candidate materials are phenols,hydroquinone, and others.

Analyte Permeable Layers and Getter Materials

In various instances, the analyte or reaction-sensitive layer, the wellor chamber or passivation opening, or adjacent structures may be furthermodified to be even more selective to the particular analyte or reactionto be detected or sensed. In some examples wherein the analyte to besensed are ions or a concentration of ions an ion-permeable layer thatis selective for the desired ions to be sensed may be formed on or overthe analyte or reaction-sensitive layer. In this case the ion permeablepreferentially lets ions of interest pass through it to interact withthe analyte or reaction-sensitive layer while not allowing or at leastreducing the number of ions that are allowed to pass through it, whichions are not of interest. Furthermore, In other instances, a “getter”material that “gets” or sequesters unwanted ions may be placed on thepassivation surface, well or chamber sidewalls, lid of the packagesensor chip or other surfaces with the purpose of sequestering or“getting” unwanted ions or analytes away from the sensing region so thatthey do not interfere with the proper sensing of the analyte or reactionof interest.

Passivation Layer

In various instances, a passivation layer may be disposed on the surfaceand/or channel, such as layered or otherwise deposited on the 1D, 2D, or3D nanomaterial layer and/or on an associated reaction or analyte orreaction-sensitive layer on the surface and/or channel. Such apassivation layer may have a thickness of about 5 microns or less, suchas about 3 microns or about 1 micron or about 0.5 microns, such as about0.1 microns or less. The passivation layer may be formed of an inorganicmaterial, such as an oxide, nitride, carbide, or mixtures thereof or maybe formed of an organic material, such as a polymer, e.g., polyimide,PBO or BCB.

ChemFET Well or Passivation Opening

In particular instances, the primary and/or secondary and/or tertiarylayers or structures may be fabricated or otherwise configured so as toinclude a chamber or well structure or opening in and/or on thepassivation surface. For instance, a well structure may be positioned ona portion of a surface, e.g., an exterior surface, of the primary and/orsecondary structures, such as over or adjacent to a channel regionwithin one or more of the structured layers. For example, in someinstances, the well structure may be formed on top of, over or mayotherwise include, at least a portion of the 1D, 2D, and/or 3Dnanomaterial, and/or may additionally include the reaction or analyte orreaction-sensitive, e.g., oxide, and/or passivation layers. In variousinstances, the chamber and/or well structure may define an opening, suchas an opening that allows access to an interior of the chamber, such asallowing direct or indirect contact or coupling with the 1Dnanomaterial, e.g., carbon nanotube or nanowire, 2D nanomaterial, e.g.,graphene, or 3D surface and/or channel or direct contact with a reactionor analyte or reaction-sensitive layer that is on or over thenanomaterial channel. In other instances, the passivation layer may berelatively thin (e.g., on the order of 1 micron or less) and openings inthe passivation layer create exposed surfaces of the 1D or 2Dnanomaterial or reaction-sensitive material without creating structuresthat might be considered wells or chambers. In either such instances,the ChemFET device may be configured so that a solution or fluid is usedto transport reactants to the well/chamber or exposed surfaces.

ChemFET Gate

The fluid or solution used to transport reactants to the well/chamber orexposed surfaces may also be used to supply a gate voltage to theChemFET device (e.g., a probe or electrode, such as a referenceelectrode, having a controlled voltage communicates with the fluid orsolution to imply its voltage on the fluid or solution) as a solutiongated sensor device. The reference or solution gate electrode may beimplemented as a separate element communicating with the fluid orsolution or may be incorporated on the sensor chip or in the sensor chippackage.

In some instances, it is advantages to have a dual gate on the ChemFET,such as a solution gate and a backgate. The backgate would allow a gatevoltage to be applied to the ChemFET from an opposite direction from thesolution gate, e.g., the solution gate may be on top of or over thechannel and the backgate may be under the channel. The backgate may beimplemented as a global backgate (voltage applied globally to theprimary base substrate) or as a local backgate (voltage applied locallyin the channel region, e.g., through use of a conductive electrode orinterconnect configured to supply the backgate voltage). The combinationof both a backgate and solution gate used in concert, i.e., a dual gate,can lead to improved ChemFET sensitivity—even beyond the Nernst limit of59 mV/pH.

In other instances, the ChemFET channel may be exposed or suspended suchthat the gate can surround a portion of the channel, i.e., in the caseof a solution gate the solution would surround a portion of the channel,providing a Gate All-Around (GAA) structure. Dual gate or GAA structuresoffer the benefit of better channel control and for sensors may alsoimprove the sensitivity and accuracy.

Manufacturing Processes for Gate All Around ChemFET

A typical nanomaterial-based ChemFET has a conductive source, aconductive drain, a nanomaterial channel such as graphene, a wellstructure and associated chamber, a fluid and a gate voltage appliedthrough the fluid such as applied by a gate or reference electrode inorder to form a nanomaterial-based, solution-gated ChemFET. The ChemFETmay In some instances, include an analyte or reaction-sensitive layer,which may further improve the sensitivity of the ChemFET for detectionof certain analytes or chemical reactions or biologic activity.

An improvement over the typical ChemFET just described to is provide asecond gate, i.e., a backgate for the device such that the backgate andsolution gate can both apply voltages to the channel in a dual-gatefashion. Having two gate voltages, on opposite the other around thechannel has the advantage of more precisely controlling the ChemFETwhich in turn leads to better sensor sensitivity.

An even more enhanced example of this concept is to completely surrounda portion of the channel with gate material so that the whole channelcircumference in some portion of the channel is fully enclosed by thegate material. This gives the highest degree of control over the channelthrough the gate all around structure.

A gate all around ChemFET is included of a conductive source, conductivedrain, channel, such as a graphene channel, an optional analyte orreaction-sensitive layer over the channel, a well structure providing achamber that holds a fluid wherein a gate or reference electrode appliesa gate voltage to the fluid. In the gate all around example thedielectric and metal under a relatively large portion of the channelregion have been removed, such as by etching. In this fashion the fluidis free to flow over, under and around the exposed portion of thechannel—hence forming a gate all around structure.

In one instance, the gate all around structure is achieved by providingan etch stop structure configured as a tub-like shape and positioned inthe dielectric material under the channel. A wet chemical etch can beused to remove the dielectric layer under the channel and within theetch stop layer-defined tub. In this example the etch is preferably awet chemical etch and not a dry, e.g., plasma, etch since dry etchprocesses tend to damage or destroy the graphene. A suitable wet etchantis a hydrofluoric (HF) acid-based etchant, such as a mixture of HF and abuffer such as ammonium fluoride. This etchant has high selectivity tosilicon dioxide in comparison to silicon and thus silicon of the sensorIC chip wafer should not be damaged. Furthermore, an HF-based etchshould not have bad effect on the graphene channel.

In a second instance of the preferred gate all around structure, thegraphene is first deposited or formed on a metal interconnect materialthat may form one of the source or drain conductive electrodes. If theinterconnect material is copper, such as formed in trenches in adamascene process and with the upper portions of the electrodes exposedto the surface, i.e., copper is exposed to the surface then thepossibility exists for forming the graphene (i.e., growing the graphene)directly on the semiconductor IC wafer rather than on a separate growthwafer and then transferring the graphene to the IC wafer. This may bepossible since copper is one of the preferred growth substrates forgraphene (graphene does not diffuse into copper during the growth) andif the growth temperature is kept low enough, such as lower than 400 C,so as not to affect the semiconductor transistors, such as CMOStransistors.

It may be possible that a plasma-enhanced CVD (PECVD) or other enhancedCVD process will allow growth of good quality graphene directly on theexposed copper surfaces on an IC wafer. Once the graphene is formed ordeposited on the copper areas then in a subsequent process step thedielectric underlying the channel area, which at this time includes bothgraphene and a thin layer of copper, is etched. For a silicon dioxidedielectric, a wet HF acid etchant is suitable. The etch may be furthercontrolled or confined by an etch stop layer formed in a tub-like shapeunder the channel. Finally, the thin copper layer under the graphenechannel can be etched by a suitable copper etchant, such as ammoniumpersulfate or ferric chloride, resulting in the central portion of thegraphene channel to be free of any dielectric, or metal and availablefor contact by the fluid to form a gate all around structure.

In another gate all around example there is no etch stop layer providedunder the channel sensing region. In this case the wet etching of thesilicon dioxide dielectric will be isotropic and will result in abowl-shaped cavity beneath the channel. Furthermore, since the etchingis not confined by an etch stop layer, the etched cavity may not befully uniform in size and shape.

All of the process examples just discussed may result in a gate allaround structure.

Accordingly, a further aspect of the present disclosure is a biosensoror chemsensor. The biosensor or chemsensor includes a CMOS structurethat may include a conductive source, e.g., a damascene copper source,as well as a conductive drain, e.g., a damascene copper drain, a 1D or2D nanomaterial layered or 3D layered, e.g., a graphene layered, surfaceor channel extending from the source to the drain, and a well or chamberstructure or passivation opening that may be positioned on or over aportion of an exterior surface of the 1D or 2D nanomaterial channeland/or 3D layered well or an analyte or reaction-sensitive layer overthe channel.

In particular instances, the well structure or passivation opening maybe configured so as to define an opening that allows for direct orindirect fluidic contact or coupling with the 1D nanomaterial, e.g.,nanotube, nanowire, and/or 2D nanomaterial, e.g., graphene, analyte, orreaction-sensitive layer over the channel, or well or chamber orpassivation opening surface. In various instances, the well structure isfurther configured to include a 3D structural element, such asincorporated into one or more of the well bounding members. Further, anoxide and/or passivation layer may be disposed in or on the chambersurfaces. Hence, in certain instances, a ChemFET e.g., a gFET, includingone or more nano- or micro-wells may be provided.

Nanomaterial Growth and Transfer

In view of the above, in one aspect, the present disclosure is directedto a method of fabricating a ChemFET, such as a transistor having one ormore of a 1D, 2D, or 3D nanomaterial associated therewith, such as inproximity to a sensing zone configured within the ChemFET. Any suitablemethod may be employed in such a fabrication process, however, invarious instances, the method may involve the growing and/ortransferring of the one-dimensional (1D) or two-dimensional (2D)nanomaterial for use in the sensor. In such an instance, the method mayinclude the growing of the 1D or 2D nanomaterial layer, such as on asuitable growth platform, which may be a silicon platform or substrate.Particularly, the method may include releasing the 1D and/or 2Dnanomaterial layer from the growth platform and/or transferring thenanomaterial layer to the semiconductor structure or substrate.

ChemFET Sensor Array

Accordingly, in some examples, the ChemFET sensor chip may include aplurality of wells and may be configured as an array, e.g., a sensorarray. Such an array or arrays may be employed such as to detect apresence and/or concentration change of various analyte types in a widevariety of chemical and/or biological processes, including nucleic acidhybridization (e.g., DNA/DNA, DNA/RNA) and/or DNA or RNA sequencingreactions. For instance, the devices herein described and/or systemsincluding the same may be employed in a method for the analysis ofbiological or chemical materials, such as for whole genome analysis,genome typing analysis, microarray analysis, panels analysis, exomeanalysis, microbial/microbiome analysis, genotyping analysis, and/orclinical analysis, such as cancer analysis, NIPT analysis, cfDNA,blood/plasma/serum analysis, UCS (upstream conserved sequence) analysis,biomolecule analysis and/or analyte analysis.

In a particular example, one or more surfaces within the wells of theChemFET may be configured as a sensing zone, which sensing zone mayinclude an additional structure, such as a 1D, 2D, e.g., graphene, or 3Dnanomaterial layer, and hence, the FET may be a graphene FET (gFET)array. It may be noted that having multiple wells sensing the sameanalyte or reaction allows statistical improvement of the sensingresult.

Such FET sensors as herein described may be employed to facilitate DNAhybridization and/or sequencing techniques, such as based on monitoringchanges in ion concentration, e.g., hydrogen ion concentration (pH),changes in other analyte concentrations, and/or binding eventsassociated with chemical processes (e.g., relating to DNA synthesis),such as within a solution gated sensing chamber or well or passivationopening of the gFET based sensor, such as proximate the sensing zone(s).For example, the ChemFET may be configured as or coupled to a CMOS IC toform a biosensor and/or may be adapted to increase the measurementsensitivity and/or accuracy of the sensor and/or associated array(s),such as by including one or more surfaces or wells having a surfacelayered with a 1D and/or 2D and/or 3D nanomaterial, a dielectric layer,a channel layer used for sensing, an analyte or reaction-sensitivelayer, a passivation layer, and the like. In particular instances, theincreased sensitivity of the sensors may, in part, be due to thepresence of the 1D or 2D or 3D nanomaterial, and/or further enhanced byits relationship to one or more of the analyte or reaction sensitiveand/or passivation layers, which in turn allows for smaller sensorconfigurations, therefore smaller channels and/or gates, and thus agreater density of sensors and/or arrays.

ChemFET Channel Nanomaterial Growth and Transfer

For instance, in a particular example, a chemically-sensitive ChemFET isprovided, where the ChemFET sensor, e.g., biosensor, may include asemiconductor substrate, such as a silicon wafer with CMOS circuitry,and at least a first dielectric layer that may itself be configured soas to incorporate one or more of a 1D, 2D, and/or 3D nanomaterialchannel structure therein. For example, a 1D nanomaterial structure,such as a CNT or a Si NW grown or formed separately from the biosensorsubstrate, may be layered within, or coated on top of the dielectriclayer, such as via spin coating, casting, or other deposition method. Inanother example, a Si NW may be formed from a silicon or othersemiconductor layer that is over or on the first dielectric layer. Inthat case the silicon or other semiconductor layer may be patterned andetched to form a semiconductor NW from the bulk semiconductor layer. Thesemiconductor NW may have regions that are appropriately doped, such asby implant and diffusion of appropriate materials, to create n or p-typeregions or to create junctions.

Additionally, or alternatively, a 2D structure or nanomaterial layer maybe applied to the first dielectric layer of the semiconductor structure,such as by the growth, or release, and/or transfer of the 2Dnanomaterial thereon. Particularly, in various examples, the 2Dnanomaterial may be graphene, silicene, molybdenum disulfide, blackphosphorous (phosphorene), borophene, tungsten disulfide, boron nitride,tungsten diselenide, stanene, germanane, nickel HITP, and/or metaldichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2,Ti3CN, Nb4C3, or Ta4C3.

More particularly, in certain examples, the 2D nanomaterial may be grownand/or transferred onto the substrate and/or dielectric surface of thesemiconductor, e.g., CMOS, structure, which structure may therefore be aread-out integrated circuit (ROIC). For instance, there are severalgrowth mechanisms that may be implemented for the growth of such a 2Dnanomaterial on a growth substrate, such as including the growth on ametal plate, a metal foil, a thin film metal, or a metal, e.g., silicon,wafer, and the like. Likewise, the 2D nanomaterial may be applied to thegrowth material by chemical vapor deposition (“CVD”) (atmospheric, low,or very low pressure), PECVD, ALD, or grown in a hot wall or cold wallreactor.

ChemFET Nanomaterial Transfer

Once grown, the 2D nanomaterial may be transferred to the ROICstructured IC chip, such as by one or more of the following transfermechanisms including direct transfer from the growth substrate to a ROICwafer using Van der Waal's forces, fusion bonding, and/or usingtemporary bonding. Further, there are several release mechanisms thatmay be implemented for effectuating the release of the 2D nanomaterialfrom the growth medium and/or substrate pursuant to the transfer of the2D nanomaterial to the ROIC, which release mechanisms may includeaqueous electrolyte electrolysis, e.g., with the growth platform as thecathode, and separation due to hydrogen evolution. Another releasemechanism may be by separating a temporary adhesive from the growthplatform using a laser, a UV light, a temperature increase, or physicalpeeling or pulling, and the like.

Additionally, in various examples, the ChemFET structure mayadditionally include a further insulating layer, such as positioned ontop of the second insulating layer, which first and/or second insulatinglayer(s) may be positioned one on top of the other, such as with the 1Dor 2D nanomaterial positioned there between. In particular instances,the first and/or second insulating layers may include a well structure,such as a well or chamber having a 3D structural layer, such as withinor otherwise associated with a surface of the well or chamber. Further,in various examples, the ChemFET structure may include an analyte orreaction-sensitive layer, e.g., an oxide layer, such as a layer that isdeposited, e.g., via CVD deposition, or may be otherwise disposed on thesurface of the well or chamber so as to increase the measurementsensitivity and/or accuracy of the sensor and/or associated array(s).

The oxide layer, when present, may be composed of metal oxide, forexample, an aluminum oxide, a tantalum oxide, a hafnium oxide, and thelike. Particularly, the oxide layer may have a suitable thickness, suchas from about 100 nm to about 75 nm, from about 50 nm to about 30 nm,from about 40 nm to about 25 nm, from about 20 nm to about 10 nm or 9 nmor less, respectively. Preferably, the passivation layer may have asuitable thickness such as from about 5 microns to about 3 microns, suchas from about 2 microns to about 1 micron, from about 500 nm to about100 nm or less.

Accordingly, the present ChemFET integrated circuits, sensors, and/orarrays of the description may be fabricated such as using any suitablesemiconductor fabrication (fab) processing techniques known in the art.In certain instances, such a semiconductor processing technique may beconfigured to increase the measurement sensitivity and/or accuracy ofthe sensor and/or array, and at the same time facilitate significantlysmall channels having relatively smaller sensor sizes and denser ChemFETchamber sensor regions.

Particularly, in various examples, the improved fabrication techniquesherein described result in sensor devices containing sensing zonesemploying a 1D or 2D nanomaterial layer, and/or may include a 3Dstructural layer. For instance, a 1D or 2D nanomaterial layer may begrown, such as on a growth platform, and once grown may be released fromthe growth platform, and then be transferred to a semiconductorstructure, such as a CMOS substrate, so as to be employed as a ChemFETsensor therein.

ChemFET Fabrication with Electrode Contacts Through the Nanomaterial

Additionally, during or after manufacture one or more surfaces or layersof the ChemFET structure may be treated so as to contain one or moreadditional analyte or reaction-sensitive layers, such as an oxide layer,which structures and layers, alone or in combination provide for rapiddata acquisition, such as from small sensors to large and dense arraysof sensors. In certain examples, one or more of such layers may befabricated along with the manufacture of the array, such as via one ormore chemical vapor deposition techniques. Further, in particularexamples, an ion-selective permeable membrane layer may be included,such as where the membrane may include a polymer, such as aperfluorosulphonic material, a perfluorocarboxylic material, PEEK, PBI,Nafion, and/or PTFE.

In some examples, the ion-selective permeable membrane may include aninorganic material, such as an oxide or a glass. In more particularexamples, one or more of the various layers disclosed herein, e.g., the1D or 2D nanomaterial layer, the analyte or reaction-sensitive layer,passivation, and/or permeable membrane layers, and the like may befabricated or otherwise applied by a spin-coating, anodization, PVD,CVD, ALD and/or sol-gel method.

Accordingly, in a particular fabrication process, a method of forming anintegrated circuit, such as for use in performing a sensing, such as anucleic acid sequencing and/or detection sensing, is provided. Themethod(s) may include one or more steps of providing a semi-conductingsubstrate having a plurality of extended planar surfaces, such as a topand a bottom surface, that are offset from one another by a firstthickness, and are surrounded by one or more side members, such as acircumferential side member, if the substrate is circular, elliptical,or round, or a plurality of opposed side members contacting each otherat their edges, such as if the substrate is square, and the like. Invarious instances, the substrate may include one or more transistorelements and/or interconnects that may be positioned within thethickness between the plurality of surfaces.

Additionally, a second step may include depositing a first insulatingdielectric layer onto the top of the planar surface of the substrate sothat the dielectric layer extends at least partially across the planarsurface, such as from one side portion to another side portion, e.g.,edge to edge. A plurality of trenches, e.g., opposed trenches, may thenbe formed in the first insulating dielectric layer, such as where eachtrench is offset from the other by a distance, which distance may beconfigured so as to form a channel region.

A third step may include depositing a first layer of conductive materialinto each of the trenches so as to form an electrode within each trench.For instance, a first electrode in a first trench may be configured soas to serve as a source electrode, and a second electrode in a secondtrench may be configured to serve as a drain electrode, such as wherethe source and drain electrodes are offset by the channel region, andmay be in contact with the one or more transistor elements.

In certain instances, once the electrodes have been formed a 1D or 2Dnanomaterial layer, e.g., graphene, may be positioned over thedielectric layer in a manner to cover the source and drain electrodes aswell as the region therebetween. However, in some instances, the firstinsulating dielectric layer may be conditioned prior to depositing the1D or 2D nanomaterial layer over it, such as in a manner so that a sideand/or top surface of each of the plurality of electrodes is made toextend above the surface of the surrounding insulating dielectric layer,and in some instances, only after this conditioning is the 1D or 2Dnanomaterial, e.g., graphene, layer deposited or otherwise formed overthe insulating layer, such as onto the side and top surface of each ofthe plurality of electrodes and across the channel region to therebyform a channel between the electrodes.

In various examples, the conditioning may be accomplished by etching,such as wet or dry etching. Likewise, an additional plating and/orpolishing, e.g., electroless chemical polishing, and/or otherconditioning steps may be included, such as by being inserted betweenone or more of the other recited process steps. For example, in someexamples, after the first conductive material is added and/or the 1D or2D nanomaterial layer is to be added, one or more openings may be madein the 1D or 2D nanomaterial so as to allow the conductive electrodematerial to push through and rise above the surface of the 1D or 2Dnanomaterial layer. Such a step as this may be performed in addition toor substitution for the conditioning step. In such an instance, a secondlayer of conductive material may then be deposited on at least a portionof the 2D nanomaterial so as to contact each of the plurality ofelectrodes so that combined conductive material of each of the pluralityof electrodes extends further above the surface of the insulatingdielectric layer.

Nevertheless, where conditioning takes place, an opening of the 1D or 2Dnanomaterial layer may also take place so as to form an opening in the2D nanomaterial layer, such as proximate each electrode, so as to exposeat least the top surface of each electrode. In such an instance, asecond layer of conductive material may be deposited over each openingof the 2D nanomaterial layer so that the second layer of conductivematerial contacts the first conductive material, fills the opening, andfurther extends above the 2D nanomaterial layer so as to contact atleast one of a side and top surface of the 2D nanomaterial layer. In anyof these instances, a patterning step may take place, such as employinga mask and photoresist process, so as to pattern the 1D or 2Dnanomaterial layer forming the channel.

Additionally, in various examples, a second insulating passivationmaterial layer may be deposited over the patterned 2D nanomateriallayer, which second insulating passivation layer may itself be patternedso as to form a chamber having a bottom surface proximate the channelregion. In particular instances, this chamber may be configured as awell so as to form a sensing chamber wherein a nucleic acid sequencingreaction, a hybridization reaction, or other detection reaction, maytake place.

Consequently, in various instances, the result of these methods is theproduction of an integrated circuit chip, which as indicated above, maybe used in performing a nucleic acid sequencing and/or detectionreaction. In such an instance, the integrated circuit chip may includeone or more of a semiconducting substrate that includes a plurality ofextended planar surfaces offset from one another by a first thickness,which are surrounded by one or more circumferential or edged sidemembers, such as where the substrate may be configures as a CMOScircuit, and therefore may have one or more transistor elementspositioned between the plurality of surfaces. Hence, in particularexamples, the substrate may include an array of CMOS field effecttransistors that may be arranged in or on the substrate.

Accordingly, the substrate may form or otherwise include a primary layerthat forms a base layer for the integrated circuit. Additionally,included may be a secondary layer that is positioned over the primarylayer. Such a secondary layer may be formed of a first non-conductivematerial, so as to be a dielectric and may include a plurality oftrenches, such as where each trench is offset by a distance one from theother, where that distance forms a channel region. The trench may beconfigured so as to include an electrically conductive material so as toform an electrode, and the trench may further be configured in such amanner that a side and top surface of the electrode extends above thetop surface of the of the insulating layer. Further, each of theelectrodes may be orientated with respect to one another so as to form achannel region there between, and thus, each electrode on either side ofthe channel region may be either a source electrode or a drainelectrode.

Further, a tertiary layer may be included and positioned over thesecondary layer, such as where the tertiary layer includes a 1D and/or2D nanomaterial, which may be formed over one or more of the side andtop of the source and drain electrodes. In such an instance, the 2Dnanomaterial may be formed within or over the channel region so as toelectrically connect the source and the drain electrodes and therebyform the channel. In some examples, the structure of the integratedcircuit may include a fourth layer, which fourth layer may extend acrossthe surfaces of the second and/or third layers, and may further includea surface structure that overlaps the source and the drain in thesecondary layer. For example, the fourth layer surface structure mayrise above the second and third layers but may include a chamber thatdefines a well having sidewalls and a bottom, such as a bottom thatcorresponds with the channel region and/or extends over at least aportion of the 2D nanomaterial so as to form a sensing chamber for theperformance of a sequencing, hybridization, detection, or otherreaction.

ChemFET Sensor IC Chip and System

Accordingly, in a further aspect, a system is provided, such as a systemconfigured for running one or more reactions so as to detect a presenceand/or concentration change of various analyte types in a wide varietyof chemical and/or biological processes, including DNA hybridizationand/or sequencing and/or other detection reactions. As such, the systemmay include an array including one or more, e.g., a plurality ofsensors, such as where each of the sensors includes a ChemFET having aconductive source, a conductive drain, and a sensing surface or channelextending from the conductive source to the conductive drain. Inparticular instances, the array may include one or more wells configuredas one or more sensing chambers having the sensing surface or channelpositioned therein. In some instances, the surface and/or channel of thechamber may include a one-dimensional (1D) or two-dimensional (2D)transistor nanomaterial, a three-dimensional (3D) structural layer maybe included, as well as a dielectric or sensing layer, an ion sensitivepermeable membrane, a passivation layer, and/or the like.

The system may further include one or more fluidics components, such asfor performing the reaction, a circuitry component, such as for runningthe reaction processes, and/or a computing component, such as forcontrolling and/or processing the same. For instance, a fluidicscomponent may be included where the fluidic component is configured tocontrol one or more flows of reagents over the array and/or one or morechambers thereof. Particularly, in various examples, the system mayinclude a plurality of sensing locations, such as surfaces or wells,which in turn includes a plurality of sensors and/or a plurality ofchannels, and further includes one or more fluid sources containing afluid having a plurality of reagents and/or analytes for delivery to theone or more surfaces and/or wells for the performance of one or morereactions therein. In certain instances, a mechanism for generating oneor more electric and/or magnetic fields is also included.

The system may additionally include a circuitry component, such as wherethe circuitry component may include a sample and hold circuit, anaddress decoder, a bias circuitry, and/or at least one analog-to-digitalconverter. For instance, the sample and hold circuit may be configuredto hold an analog value of a voltage to be applied to or on a selectedcolumn and/or row line of an array of a device of the disclosure, suchas during a read interval. Additionally, the address decoder may beconfigured to create column and/or row select signals for a columnand/or row of the array, so as to access a sensor with a given addresswithin the array. The bias circuitry may be coupled to one or moresurfaces and/or chambers of the array and include a biasing componentsuch as may be adapted to apply a read and/or bias voltage to selectedChemFETs of the array, e.g., to one or more gate terminals of thetransistor. The analog to digital converter may be configured to convertan analog value to a digital value.

Computing Component

A computing component may also be included, such as where the computingcomponent may include one or more processors, such as a signalprocessor; a base calling module, configured for determining one or morebases of one or more reads of a sequenced nucleic acid; a mappingmodule, configured for generating one or more seeds from the one or morereads of sequenced data and for performing a mapping function on the oneor more seeds and/or reads; an alignment module, configured forperforming an alignment function on the one or more mapped reads; asorting module, configured for performing a sorting function on the oneor more mapped and/or aligned reads; and/or a variant calling module,configured for performing a variant call function on the one or moremapped, aligned, and/or sorted reads.

Other modules that may be included are alignment modules, variant callmodules, and any other module useful in analyzing the results ofdetection or sequencing reactions. In various examples, one or more ofthese modules may be in a hardwired configuration, for example,configured as an integrated circuit. In particular instances, the basecaller of the base calling module may be configured to correct aplurality of signals, such as for phase and signal loss, to normalize toa fiducial, internal nucleotide standard, and/or to a generate aplurality of corrected base calls for each flow in each sensor toproduce a plurality of sequencing reads. In various instances, thedevice and/or system may include at least one reference electrode.

Particularly, the system may be configured for performing a nucleic acidsequencing and/or hybridization reaction. In such an instance, the FETdevice may include an array of sensors having one or more ChemFETsassociated therewith. Such transistors may include a cascode transistorhaving one or more of a source terminal, a drain terminal, and or one ormore gate terminals, such as composed of a damascene copper. In such aninstance, the source terminal of the transistor may be directly orindirectly connected to the drain terminal of the ChemFET, such as by, aone or two dimensional nanomaterial channel or other suitably configuredsurface element that may extend from the source terminal to the drainterminal, such as where the 1D channel nanomaterial may be a carbonnanotube or semiconductor, e.g., silicon, nanowire, and thetwo-dimensional channel nanomaterial may be composed of graphene,silicene, molybdenum disulfide, black phosphorous (phosphorene),borophene, tungsten disulfide, boron nitride, tungsten diselenide,stanene, germanane, nickel HITP, and/or metal dichalcogenides or Mxenessuch as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2, Ti3CN, Nb4C3, or Ta4C3.

Read Out Integrated Circuits

The device may further be configured to include a plurality of columnand row lines coupled to the sensors in the array of sensors. In such aninstance, each column line in the plurality of column lines may bedirectly or indirectly connected to or otherwise coupled to the drainterminals of the transistors, e.g., cascode transistors, of acorresponding plurality of sensors and/or pixels in the array, andlikewise each row line in the plurality of row lines may be directly orindirectly connected to or otherwise coupled with the source terminalsof the transistors, e.g., cascode transistors, of a correspondingplurality of sensors in the array. In some instances, the sensors insuch an array may be independently addressable.

In some instances, a plurality of source and drain terminals having aplurality of sensing surfaces, e.g., channel members, extended therebetween may be included, such as where each channel member includes aone or two or even three-dimensional material. In such an instance, aplurality of first and/or second conductive lines, and so forth, may becoupled to the first and second source/drain terminals of the ChemFETsin respective columns and rows in the array, and so forth. Additionally,control circuitry may be provided and coupled to the plurality of columnand row lines such as for reading a selected sensor connected to aselected column line and/or a selected row line. The circuitry may alsoinclude a biasing component having a bias circuitry such as isconfigured to apply a read voltage, while a sample and hold circuit maybe configured to hold an analog value of a voltage on a selected columnline of the array during a read interval.

Particularly, the bias circuitry may be configured for applying a readvoltage to the selected row line, and/or to apply a bias voltage such asto a gate terminal of a transistor, such as FET and/or cascodetransistor of the selected sensor. In a particular example, the biascircuitry may be coupled to one or more chambers of the array and beconfigured to apply a read bias to selected ChemFETs via the conductivecolumn and/or row lines. Particularly, the bias circuitry may beconfigured to apply a read voltage to the selected row line, and/or toapply a bias voltage to the gate terminal of the transistor, e.g.,cascode transistor, such as during a read interval.

A sense circuitry may also be included and coupled to the array so as tosense a charge coupled to one or more of the gate configurations of aselected ChemFET. In some instances, the sense circuitry may sense avoltage level or a current level of a selected ChemFET. The sensecircuitry may be configured to read the selected sensor based on asampled voltage level on the selected row and/or column line. In such aninstance, the sense circuitry may include one or more of a pre-chargecircuit, such as to pre-charge the selected column line to a pre-chargevoltage level prior to the read interval; and a sample circuit such asto sample a voltage level at the drain terminal of the selectedtransistor, such as during the read interval. A sample circuit mayfurther be included and contain a sample and hold circuit configured tohold an analog value of a voltage on the selected column line during theread interval, and may further include an analog to digital converter toconvert the analog value to a digital value.

In particular examples, the computer component of the ChemFET sensor ICchip structure may include a processor configured for controlling theperformance of one or more reactions involving a biological or chemicalmaterial so as to obtain reaction results, and for analyzing thoseresults, for instance, based on detecting and/or measuring changes in avoltage (V) potential, current (I), charge (Q) or capacitance (C)occurring on or near the ChemFET. Particularly, the processor, such as amicroprocessor, a microcontroller, or a signal processor, may beconfigured so as to generate one or more current (I) vs. voltage (V)curves, such as where the current I of the I-V curve is the currentflowing at the drain of the ChemFET and/or where the gate voltage (Vgs)of the I_(d)-V_(gs) curve is a gate voltage applied between the gate andsource of the ChemFET. In such an instance, the gate voltage Vgs of theI_(d)-V_(gs) curve may be a top, e.g., solution, and/or a back gatevoltage that may be applied to the ChemFET through a top (or front)and/or back of the device, respectively.

In particular instances, a suitably configured device of the disclosuremay be adapted as a front and/or back-gated device, which may further beconfigured as a solution gate. Accordingly, in various examples, adevice of the disclosure may be a field-effect transistor that includesa chamber adapted for measuring ion concentrations in a solution; suchas where, when the ion concentration (such as H+ or OH− in a pH scale)within the chamber changes, the current through the transistor, e.g., achannel region thereof, will change accordingly. In such an instance,the solution, when added to the chamber forms, or otherwise serves as, agate electrode.

Hence, in specific examples, the gate voltage Vgs of the I_(d)-V_(gs)curve may be a solution gate voltage such as applied to the ChemFETthrough a solution flowed over a portion, e.g., a chamber, of thedevice. In some examples, a reference I_(d)-V_(gs) curve and/or achemical sensing I_(d)-V_(gs) curve may be generated in response to thebiological activity, analyte material and/or chemical reaction that isto be detected and/or occurs over or near the ChemFET, such as within achamber or well of the FET structure. In various examples, the processormay be configured to determine differences in relationships between apredetermined or generated reference I_(d)-V_(gs) curve and/or chemicalsensing I_(d)-V_(gs) curve. In certain instances, the circuitrycomponent may include at least one analog-to-digital converter that isconfigured for converting analog signals, such as obtained as a resultof the performance of the reaction(s) within the sensing well, or arrayof wells, into digital signals.

Accordingly, in another aspect, a ChemFET device may be provided,wherein the device may include a structure having a conductive sourceand drain as well as having a surface or channel or other functionallyequivalent surface structure extending from the conductive source to theconductive drain, such as where the surface or channel may include aone-, two-, or three-dimensional transistor nanomaterial. The device mayalso include a processor such as where the processor is configured forgenerating or otherwise determining, e.g., via a look-up-table, areference I_(d)-V_(gs) curve and/or generating a chemical sensingI_(d)-V_(gs) curve, in response to the chemical reaction occurringwithin a chamber of the chemically-sensitive field effect transistor,and may be configured to determine a difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve.

In some instances, the difference between the reference I_(d)-V_(gs)curve measurement and the chemical sensing I_(d)-V_(gs) curvemeasurement is a shift in a minimum point of the Vg value of thechemical sensing I_(d)-V_(gs) curve relative to a minimum point of theVg value of the reference I_(d)-V_(gs) curve. In other instances, thedifference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve is a shift in an Ion value of the chemicalsensing I_(d)-V_(gs) curve relative to an Ion value of the referenceI_(d)-V_(gs) curve, for instance, where the Ion values are taken from ap-type or n-type section of the I_(d)-V_(gs) curve. For example, themeasurements of the slopes (one type of parameter of an I_(d)-V_(gs)curve) may be taken from the steepest and/or flattest sections on thep-type and/or n-type portions of the I_(d)-V_(gs) curves.

In particular instances, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve is ashift in an Ioff value (another representative I_(d)-V_(gs) curveparameter) of the chemical sensing I_(d)-V_(gs) curve relative to anIoff value of the reference I_(d)-V_(gs) curve. In one example, thedifference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve is a change in the slope of the chemicalsensing I_(d)-V_(gs) curve relative to a change in the slope of thereference I_(d)-V_(gs) curve. In another example, the difference betweenthe reference I_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs)curve is an overall change in shape (another I_(d)-V_(gs) curveparameter) of the chemical sensing I_(d)-V_(gs) curve relative to anoverall change in shape of the reference I_(d)-V_(gs) curve.

In other examples, the difference in overall shape of the I_(d)-V_(gs)curves is determined by first fitting a polynomial or other fitting lineto each of the I_(d)-V_(gs) curves and then comparing the coefficientsof those fitting lines. In other examples, the difference between areference I_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curveis based on more than one chemical sensing I_(d)-V_(gs) curve.

Accordingly, in particular examples, the FET and/or processor may beconfigured to respond to a shift in the I-V or I_(d)-V_(gs) curve, suchas where the curve is shifted in response to the detection of ananalyte, biologic activity and/or the result of a reaction taking placenear or on a surface of the FET device. In some instances, theI-V/I_(d)-V_(gs) curve may be produced and/or shifted in response to achemical reaction occurring proximate to a sensing layer and/or thesurface of a 1D or 2D nanomaterial, e.g., graphene, surface of the fieldeffect transistor, such as resulting from the detection of a biologicalcompound or reaction occurring within the well structure of the device.Hence, the FET and/or processor may be configured so as to shift thereference I-V curve or chemical sensing (or “test”) I_(d)-V_(gs) curvesuch as in response to the chemical reaction.

In various examples, one or more elements and/or methods, as hereindescribed, may be used to shift a reference I-V or I_(d)-V_(gs) curveand/or a chemical sensing I_(d)-V_(gs) curve so that the differencebetween the reference I_(d)-V_(gs) curve and a chemical sensingI_(d)-V_(gs) curve is more pronounced. For instance, the device mayinclude a structure, such as a membrane, other surface layer, and/orother element configured for enhancing the ability of the processor todetermine the difference between various I-V and/or I_(d)-V_(gs) curves.

Hence, in a further aspect, a ChemFET transistor that is fabricated on aprimary structure having a stacked configuration including one or moreof an inorganic base layer, e.g., a silicon layer; a dielectric and/oran organic or inorganic dielectric layer, such as a silicon dioxidelayer; a 1D, 2D, or 3D nanomaterial layer, such as a carbon nanotube,nanowire, or graphene layer; an analyte or reaction-sensitive layer,e.g., oxide layer and a passivation layer; and further having aconductive source and drain embedded in one or more of the layers, withthe nanomaterial forming a channel between the source and drain, and agate structure, e.g., a solution gate region, may be provided. Invarious examples, the sensing region may be configured so as to form achamber or well and the 1D or 2D nanomaterial and/or oxide layers may bepositioned between the conductive source and drain in such a manner asto form a bottom surface of the chamber. The structures may furtherinclude or otherwise be associated with an integrated circuit and/or aprocessor, such as for generating and/or processing generated data, suchas sensor derived data.

Ion Permeable Layer and Ion Getter

In particular examples, a further structured layer, e.g., a secondary ortertiary structure, may also be provided, such as where the furtherstructured layer may be included and/or present within the well orchamber, such as to enhance the ability of the processor to determinethe difference between the current and/or voltages as well as theirrespective associated curves. Particularly, the additional structure mayinclude an additional layer, e.g., an ion-selective permeable membrane,such as an ion-selective permeable membrane that allows ions of interestto pass through the membrane while blocking other ions, such as toenhance the ability of the processor to determine the difference betweenthe reference I-V or I_(d)-V_(gs) curve and the chemical sensing I-V orI_(d)-V_(gs) curve (or corresponding parameters thereof), and thusenhance the ability of the processor to detect a desired chemicalreaction.

In various instances, the FET may be configured such that the I-V orI_(d)-V_(gs) curve (s) may be shifted so as to better respond to,detect, and/or otherwise determine a biological compound and/or achemical reaction, such as a biological compound and/or a chemicalreaction occurring on or near the 1D or 2D nanomaterial, e.g., graphene,surface of the ChemFET. In particular instances, the ion-selectivepermeable membrane may include a 2D transistor nanomaterial, e.g.,graphene, which may or may not be electrically connected to the sourceand/or drain layer and/or channel.

Accordingly, in various instances, the ion-selective permeable membranemay be positioned within the well and/or over a passivation layer, anion sensitive or sensing layer, a 1D and/or a 2D transistor nanomateriallayer, and/or a dielectric layer that itself may be positioned overand/or otherwise form a part of the chamber or channel. In certainexamples, the membrane layer or an additional structural layer may be,or otherwise be associated with, an ion getter material. Such an iongetter material may be any suitable material that traps ions that maynot be relevant to the biological species, biologic activity and/orchemical reaction to be sensed and/or determined, such as to enhance theability of the processor to determine the difference between thereference I-V or I_(d)-V_(gs) curve and/or the chemical sensing I-V orI_(d)-V_(gs) curve (or corresponding parameters thereof), e.g., becausethere are fewer interfering ions, thus enhancing the ability of theprocessor to detect the desired biological species and/or results of thechemical reactions.

Particularly, the ion getter material may be arranged within proximityto the chamber and/or surface thereof so that the action of gettering(or sequestering) the unwanted ions improves the detection capability ofthe ChemFET. In some instances, one or more of the various layersherein, such as the ion getter material may be placed over one or moreof the other layers, such as the dielectric layer, oxide layer, or 1D or2D or 3D nanomaterial layers, positioned in proximity to one or more ofthe chambers, channels, or surfaces of the FET device.

For instance, a ChemFET of the disclosure may include a secondary ortertiary structure that includes a 2D nanomaterial transistor channel orsurface that may include an ion-sensitive material over the channel orsurface. In such an instance, the material may be sensitive to ions thatare different from the ions associated with the biological molecule orchemical reaction that is to be detected. Particularly, in someinstances, the action of sensing ions that are different from the ionsassociated with the biologics and/or chemical reactions that are to bedetected allows the processor to filter out the signal from the unwantedions from the signal of the ions of interest thereby decreasing theoverall noise in the system.

Charge Trap Screening Material

In particular instances, an additional material, e.g.,hexamethyldisilazane (HMDS), parylene, hexagonal boron nitride (hBN),aluminum oxide or other material, may be included so as to manage theinteraction of the channel and/or associated 1D or 2D or 3D nanomaterialtransistor layer with the dielectric layer under the channel ornanomaterial. It is known in the art that certain dielectrics,particularly such as silicon dioxide, when adjacent to a channel maytrap charges and interfere with the ideal functioning of the channel,such as by creating noise in the FET.

Alternate dielectric materials, and especially materials that may besmooth and have lattice parameters similar to the 1D or 2D nanomaterialof the channel, can significantly reduce the charge trapping effect. Inparticular when the channel nanomaterial is graphene then hBN is a goodmaterial choice (both materials have a lattice parameter of about 2.5angstroms) to attenuate any charge trapping and thus reducing the noisegenerated in the ChemFET.

Fluidics Component

In a further aspect of the present disclosure, systems having achemically-sensitive transistor, such as a ChemFET including one or morechambers, e.g., a plurality of chambers having a well structure(s)formed therein is provided. In such an instance, the well(s) may bestructured as a sensing location, wherein one or more chemical reactionsmay take place or one or more analytes may be detected or biologicactivity may be sensed. In such an example, the system may include afluidics component having a fluid source, e.g., a reservoir, containingone or more fluids therein and configured for delivering the fluid fromthe reservoir to the sensing chamber, such as for the detection of abiologic and/or the performance of one or more chemical and/orbiological reactions, such as a nucleic acid sequencing reaction. Hence,the fluidics component, e.g., the fluid source, may be in fluidiccommunication with the FET device configured for biological and/orchemical analysis.

Use of Magnetic or Electric Fields to Position Microbeads

Accordingly, in certain instances, the fluid may include one or morereactants, such as one or more components necessary for performing asequencing and/or detection reaction, as herein described. In aparticular example, the fluid may include one or more, e.g., aplurality, of microbeads or particles having nucleic acid templatesattached thereto, for instance, where the template is complementary to aportion of, and thus hybridizes to, a DNA or RNA molecule to besequenced or detected, and the fluid containing the microbead is to bedelivered to the well such as for carrying out the sequencing reaction.In such examples, one or more of, e.g., each, of the plurality ofmicrobeads or particles may be configured so as to have electric chargeand/or paramagnetic properties.

The device may additionally include an electric and/or magnetic fieldcomponent, e.g., having an electric and/or magnetic field generator,such as where the electric and/or magnetic field component is configuredto generate an electric and/or magnetic field so as to interact with theelectric and/or magnetic charge properties of each of the plurality ofmicrobeads or particles to attract them into a sensing location, such asa sensing surface, a channel, a well, a chamber, and/or a sensor of theFET device, such as by using electrophoresis and/or magnetism.

Hence, one or more, e.g., a plurality of microbeads, may be drawn ontoor into a sensing location of the plurality of sensing locations, whichlocations may be formed as wells and/or chambers, e.g., one or more thinwells or deep chambers. The microbeads may include a reagent such as abiological material or a chemical material, e.g., one or more nucleotidesequences. Particularly, a fluid including the reagent, such ascontaining microbeads containing the reagent, may be introduced into thewells and/or chambers, such as by a fluidics component of thedisclosure.

Accordingly, the reagent may be a nucleic acid sequence having negativecharge properties and/or the reagent may be coupled to a magnetic micro-or nano-bead, as such, in certain examples, an electric and/or magneticfield may be applied individually or collectively to the wells and/orchambers, so as to draw the reagent, e.g., a reagent containingmicrobead, onto each sensing location, e.g., into each well, chamber,and/or or sensor containing channel. In various instances, the electricand/or magnetic field component generates an electric and/or magneticfield so as to interact with the electric charge properties of thereagent and/or microbeads, thereby drawing it to the sensing location.In certain instances, the microbeads or particles themselves may becharged and/or may have electric and/or paramagnetic properties, andthereby may be drawn to the sensing location using electrophoresisand/or magnetism.

The use of electrophoresis and/or magnetism allows for thinner sensinglocation structures. In particular instances, therefore, an electricand/or magnetic field generator may be configured for drawing and/orpositioning a microbead or particle within the well structure, such asin proximity to a channel or chamber of the device, and in otherinstances, the electric and/or magnetic field generator may beconfigured for reversing the electrical and/or magnetic field so as torepulse the microbead or particle from the sensing location, channel,and/or chamber. In various instances, an array of sensing locations maybe provided each having a magnet that allows for selective filling ofthe sensing locations with different numbers and/or types of reactantsand/or microbeads, such as at select sensing locations. In such aninstance, multiple electric and/or magnetic field generators forselective filling of sensing locations, e.g., wells, may be provided.

Accordingly, one aspect of the present disclosure concerns systemsand/or methods for positioning one or more, e.g., a plurality, ofreactants and/or microbeads, e.g., containing one or more DNA and/or RNAtemplates attached thereto, within a sensing or plurality of sensinglocations for biological or chemical analysis, such as for nucleic acidsequencing and/or detection. Such a system may include a CMOS FET devicehaving an integrated circuit structure configured for performing abiological or chemical analysis, such as within a plurality of nano- ormicro-sensing wells, as described above, having a fluidic component, acircuitry component, and/or a computing component, and the method mayinclude one or more of the following steps.

For instance, the method may include the fluidic component introducing afluid to be in contact with the device, such as where the fluidicscomponent is configured to control a flow a fluid of reagents over thearray, and where the fluid may include one or more microbeads orparticles that may have electric charge and/or paramagnetic properties.In such an instance, the device may include an integrated circuitstructure, a plurality of sensing locations having one or more chambersand/or wells, a plurality of sensors and/or a plurality of channels,and/or an electric and/or magnetic field component.

The electric field and/or magnetic field component may be configured toactivate the electronic and/or magnetic field, and the method may alsoinclude activating an electric and/or magnetic field so as to interactwith the electric and/or paramagnetic properties of each of themicrobeads. The method may additionally include drawing the one or moremicrobeads or particles into a sensing location of the plurality ofsensing locations using electrophoresis and/or magnetism. In certaininstances, the method may include positioning the one or more microbeadsand/or particles within the one or more sensing locations for biologicalor chemical analysis.

In particular instances, the electric and/or magnetic fields may begenerated by the plurality of electric and/or magnetic field generators,e.g., included in the integrated circuit structure, in all or only asubset of the plurality of sensing locations so as to only attract aplurality of microbeads to the subset of sensing locations, such as forselectively filling the plurality of sensing locations with theplurality of microbeads. In such an instance, different types ofmicrobeads may be attracted to different sensing locations, such as bypulsing the voltage and/or magnetic generators and/or keeping the sameconstant.

Particularly, where an electric field generator is provided the voltageapplied to the device may be variable or constant and may be less thanabout 10V, such as about less than 8V, or less than about 6V, includingless than about 4V or about 2V or 1V. The voltage may be applied betweena location above the fluid and a location on or below the sensinglocation, such as above the package lid and/or below the metal platebelow the package. In certain instances, the location below the sensinglocation may be a metal or conductive layer such as within the packageor package substrate. The methods may also include the step of reversingthe electric or magnetic field so as to eject the plurality of bead orparticles from the plurality of wells, sensors, and/or channels, eitherentirely or selectively.

Further, as indicated, each or a subset of the plurality of sensinglocations may be utilized in correspondence with generating electricfields to attract a microbead or particle into or proximate the sensinglocation, thereby allowing for programmability or addressing capabilityto each or a subset of sensing locations, for instance, 99% or 95% or90% or 85%, or 80% or less of the plurality of wells are occupied with amicrobead and/or particle or other sensing location.

Additionally, in another aspect of the disclosure, a device, system,and/or method for verifying well occupancy for a plurality of wells orchambers for analysis of biological or chemical materials may beprovided. For instance, a device of the system may include a pluralityof wells or chambers being associated with a plurality of sensors, suchas where each well or chamber includes or is otherwise associated withor configured as a chemically sensitive FET. In such instances, thesystem may include a device for receiving a fluid containing theplurality of microbeads, particles, reactants, and/or other carrierscompatible with microfluidic fluid flow in automated chemical/biologicalanalysis devices.

Particularly, the ChemFET IC chip may include a processor, asemiconductor IC structure, e.g., a CMOS structure having an integratedcircuit, a plurality of wells and/or chambers, and a plurality ofsensors within the IC chip structure. Each of the plurality of wells orchambers may be configured to receive a microbead or particle of theplurality of microbeads and/or particles, and the ChemFET sensor IC chipstructure may include a mechanism for drawing and/or ejecting themicrobeads or particles into or out of the wells. Hence, the method mayinclude the step of flowing the plurality of microbeads and/or particlesover and/or into the plurality of sensing locations and/or wells and/orchambers and/or may include determining, e.g., through electrical and/ormagnetic sensing if a sensing location and/or well and/or chamber isoccupied or unoccupied and/or if a sensing location contains one ormultiple microbeads.

Consequently, the processor may be configured to determine if alocation, e.g., a well and/or chamber, is unoccupied and/or if the welland/or chamber contains one or more, e.g., multiple microbeads. Incertain instances, the processor may also be configured to eliminate ormodify one or more of the measurements, such as based on the number ofwells and/or chambers occupied or unoccupied, e.g., the number of wellscontaining none, one or multiple microbeads. For instance, the processormay be configured to eliminate from the measurement the number of wellsand/or chambers unoccupied and the number of wells and/or chamberscontaining multiple microbeads, or compensate in the measurement for thenumber of wells and/or chambers unoccupied and the number of wellsand/or chambers containing multiple microbeads, and the like. Suchcompensation can be provided as part of a calibration step of a ChemFETsensor IC chip prior to its use. The results of the calibration step maybe recorded and referred to a later time when the ChemFET sensor IC chipis being used for detection or analysis of an analyte, chemicalreaction, or biologic activity.

Representative Aspects And Examples

Accordingly, provided herein are devices, systems, and methods ofemploying the same for analysis of biological or chemical materials.Particularly, the devices, systems, and methods of the disclosure aredirected in part to 1D, 2D, or 3D nanomaterial channel ChemFET sensors,integrated circuits, and arrays employing the same for analyte,reaction, or biologic activity measurements. The present ChemFETsensors, arrays, and integrated circuits may be fabricated usingconventional semiconductor, e.g., CMOS, processing techniques based onimproved 1D, 2D, or 3D nanomaterial ChemFET sensor and array designsthat increase measurement sensitivity and accuracy, and at the same timefacilitate significantly smaller sensor sizes and dense sensor arraydesigns and real-time detection.

ChemFET Structure

Generally, a ChemFET device will include a conductive source and aconductive drain in or on a dielectric material, a channel extendingbetween the source and drain, e.g., included of a 1D or 2D nanomaterial,that functions as a sensing layer, an insulating passivation layer withan opening or well on or over the channel and a gate to control theconductance of the channel. In some examples the ChemFET may alsoinclude an analyte or reaction sensitive material layer over or on thenanomaterial channel.

One aspect of the present disclosure is a ChemFET that is fabricated ina stacked configuration including a primary structure, such as a wafer,e.g., a silicon wafer, as well as one or more additional structures. Forinstance, a dielectric material layer may also be included andpositioned on top of the primary structure, and may be an inorganicmaterial. The first and/or second structures may further be configuredto include an additional structure or structure layer that includes oneor more of a conductive source and a conductive drain. The conductivesource and the conductive drain may be orientated so as to be separatedone from another by a space, which space may be spanned by a ChemFETchannel made of a 1D or 2D nanomaterial.

The source, drain, and channel can be embedded in the primary and/orsecondary structures and/or may be planar or non-planar with a topsurface of the secondary structure or a further layer or structureassociated therewith. In various examples, the structures furtherinclude a processor, such as for processing generated data, such assensor-derived data. Accordingly, the structures can be configured as,or otherwise include, an integrated circuit chip, and/or may be a ROIC,an ASIC, a structured ASIC, or an FPGA.

For instance, as can be seen with respect to FIG. 1B (side sectionalview) and FIG. 1C (top-down view), a 2D nanomaterial layered substrate(1), such as a graphene layered substrate, for a ChemFET, such as for asystem for the analysis of chemical and/or biological materials, isprovided. The layered substrate (1) includes a primary base structure(10), such as composed of a semiconductor material such as silicon. Invarious examples, the semiconductor-based primary base structure (10)can be configured to support a semiconductor, e.g., CMOS, construct. Theprimary base structure (10) can support one or more additionalstructures such as a dielectric material layer (20). For example, thelayered substrate (1) may be in a stacked configuration such as where asecondary structure, e.g., including a dielectric material (20), isdeposited, or otherwise fabricated on top of the primary base structure(10). The secondary structure includes conductive interconnects (23)located in or on the dielectric material (20).

The primary base structure (10) and/or dielectric layers (20) mayfurther include a channel region (26) having a channel 30 that extendsfrom a conductive source (22) to a conductive drain (24), the conductivechannel included of a 1D transistor material, e.g., SiNW or CNT or a 2Dtransistor material, e.g., graphene. For instance, the stackedstructured layers are configured to include a channel region (26), whichin turn may be adapted as the sensing layer. Particularly, in certaininstances, the dielectric layer (20) includes a channel (30) and aconductive source (22) and a conductive drain (24), wherein the sourceand drain are separated from one another by a space that is spanned bychannel region (26), which source and drain may be, in this instance,planar with a top surface (21) of the dielectric layer (20). The source(22) and drain (24) are conductive and may be made of metal, such asaluminum or copper or other conductor such as polysilicon. In variousexamples, the dielectric material is an organic or an inorganicmaterial. In some examples, the organic material is a polymer,polyimide, BCB, PBO or other like material. In other examples, theinorganic material may be a silicon oxide, e.g., a silicon dioxide, or asilicon nitride or other oxide, carbide or nitride or mixtures thereof.

In particular examples, the layered structures are configured as asemiconductor device, such as a CMOS device, further configured with aChemFET containing one or more of a conductive source (22), a conductivedrain (24), and a channel 30. In some examples, a processor may beoperably associated with the ChemFET. For instance, the ChemFET (1) chipmay include a CMOS structure having an integrated circuit that isfabricated on a silicon wafer (10), which further includes a silicondioxide dielectric layer (20), including a conductive damascene coppersource (22) and a conductive damascene copper drain (24), which areembedded in or on at least the dielectric layer (20). In variousinstances, the structures may include a surface (21), e.g., a topsurface, which surface may include the channel region (26), such aswhere the surface and/or channel region may be configured as a sensingzone (26) that extends from the conductive source (22) to the conductivedrain (24).

An exemplary length of the sensing surface and/or channel region (26)from the source to the drain may range from about 0.001 microns to about10 microns, such as from about 0.01 microns to about 5 microns, forinstance, from about 0.05 micron to 3 microns, including about 0.1 orabout 0.5 microns to about 1 or about 1.5 or about 2 microns. Anexemplary width of the surface and/or channel from side to side mayrange from about 0.001 microns to about 10 microns, such as from about0.01 microns to about 5 microns, for instance, from about 0.05 micronsto 3 microns, including about 0.1 or 0.5 microns to about 1 or about 1.5or about 2 microns.

In certain examples, the surface and/or channel region may form asensing layer (26) that include a chemically-sensitive 1D or 2Dnanomaterial transistor layer (30) forming a channel. Accordingly, invarious examples, a 1D transistor material may be included, which 1Dnanomaterial can be composed of a carbon nanotube or a semiconductornanowire. In other examples, a 2D transistor material is included, which2D nanomaterial may be a graphene layer, silicene, molybdenum disulfide,black phosphorous (phosphorene), borophene, tungsten disulfide, boronnitride, tungsten diselenide, stanene, germanane, nickel HITP, and/ormetal dichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C,Ti3C2, Ti3CN, Nb4C3, or Ta4C3

For instance, in various examples, the chemically-sensitive 1D or 2Dnanomaterial transistor layer (30) may be a single layer or a 2Dnanomaterial such as a graphene. Particularly, as can be seen withrespect to FIG. 1D, graphene is a two-dimensional, monolayer of carbonatoms that are arranged as a lattice structure. This lattice structureforms regular hexagons with a carbon atom at each vertex. In such astructure, the bond length between adjacent carbon atoms is about 1.42 Åand the lattice constant is about 2.46 Å. This molecular structure isvery unique in that each carbon atom shares one of its four free valenceelectrons with three of its adjacent and planar carbon atoms such thateach of the three planar carbon atoms is orientated at about a 120° withrespect to the other three carbon atoms. Such an orientation givesgraphene its honeycomb, lattice structure. Additionally, the fourthvalence electron forms a pi bond, which may be perpendicular to thethree planar sigma-bonded carbon atoms, which is responsible for theunique electronic characteristics of graphene.

Particularly, the single-layer, two-dimensional structure of graphenegives it at least three important characteristics with respect to itsuse herein: it has a large surface area to volume ratio; it makes thegraphene layer a semimetal or ambipolar material; and it promotes rapidcharge transport (high carrier mobility) at room temperature. Hence, invarious instances, a graphene FET as herein described performs better asa biosensor or chemsensor than a typical MOSFET device not having such ananomaterial channel layer. For instance, with respect to nucleic acidhybridization detection and/or sequencing, a traditional MOSFETtransistor may have fundamental limitations in its sensitivity (due tochannel thickness and intervening insulating and interconnect layers),whereas the present FET, e.g., gFET, with its single atom thickness, canbe employed to form a solution-gated sensing zone and/or channel,wherein the graphene layer (30) may be in direct contact with or coupledto a chemical sensing zone (26) proximate. Specifically, the channellayer (30) may include a 1D or 2D transistor nanomaterial configured soas to have a much higher carrier mobility than the typical doped siliconcommonly used in MOSFET or ISFET devices. This gives the instant 1D and2D nanomaterial ChemFET-based sensor devices increased sensitivity toand faster detection of chemical reactions, analytes, or biologicactivity. Further, in various examples, the surface and/or channelregion (26) may include or include an analyte or reaction-sensitiveinsulating layer (not shown in FIG. 1B or FIG. 1C), such as for furtherincreasing sensor sensitivity and/or functioning.

Additionally, FIG. 1E depicts an alternative 2D transistor nanomateriallayer (30) that can be employed so as to increase sensitivity of thesensor so as to better enable the FET (1) to determine the presenceand/or identity of one or more reactants and/or products thereof thatresults from the occurrence of a chemical and/or biological reaction oractivity that takes place proximate to the ChemFET (1). As can be seenwith respect to FIG. 1E, the 2D nanomaterial layer in this instance ismolybdenum disulfide. Further 2D nanomaterials, as presented herein toincrease sensitivity of the sensors include a black phosphorous layer(phosphorene), as depicted in FIG. 1F, and crystalline silicon asdepicted in FIG. 1G. Alternatively, a 1D nanomaterial, such as a carbonnanotube may be employed for these enhancement purposes, such aspresented in FIG. 1H. A semiconductor nanowire structure may also beused, such as depicted in FIG. 1I for a nanowire formed separately as ananowire or as depicted in FIG. 1J for a nanowire formed by etching ordepositing of a semiconductor layer. FIG. 1J depicts a primary basesubstrate (10), e.g., a semiconductor, a dielectric layer (20), e.g., aBuried Oxide layer (BOX), and a semiconductor nanowire channel (30).

FIG. 1K depicts a layered substrate (1) configured as a ChemFET (32)comprising a primary base substrate (10), a dielectric layer (20), asemiconductor nanowire channel (30) formed by etching or deposition of asemiconductor material, a gate (12) and a gate dielectric (14) toinsulate the gate from the channel, a conductive source (22) and aconductive gate (24). The dotted line X-X is a section line that will bereferred to in other drawings. Although FIG. 1K, FIG. 1L, FIG. 1M, FIG.1N and FIG. 1O all show a conductive gate (24), such as a metal gate,over the channel region (26) it is to be understood that the gate couldalso be a solution gate in any of these examples.

FIG. 1L depicts a side sectional view of one example of thesemiconductor NW ChemFET (32) of FIG. 1K (section X-X), wherein theChemFET (32) is configured as a MOSFET. In this example thesemiconductor NW channel is doped so that an n semiconductor region(15), a p semiconductor region (16) and another n semiconductor region(15) form an n-p-n junction in the sensing region (26) of the channel.Source (22) and drain (24) contacts are provided that contact thechannel and a gate (12) is formed over the channel region (26) andelectrically isolated from the channel by a gate dielectric (14).Because the semiconductor NW width and cross-sectional area are so smallit is difficult to dope the semiconductor channel nanomaterial uniformlyand precisely, so that the MOSFET ChemFETs (32) may vary one to another.

FIG. 1M depicts a side sectional view of one example of thesemiconductor NW ChemFET (32) of FIG. 1K (section X-X), wherein theChemFET (32) is configured as a Schottky Barrier FET. In this examplethe semiconductor NW channel is not doped so that an intrinsicsemiconductor region (17) is formed in the sensing region (26) of thechannel. Conductive source (22) and drain (24) contacts are providedthat contact the intrinsic semiconductor channel forming Schottkybarrier junctions and a Schottky Barrier FET and a gate (12) is formedover the channel region (26) and electrically isolated from the channelby a gate dielectric (14). Because the semiconductor NW channel is notdoped in this example the semiconductor channel nanomaterial isrelatively uniform and precise, so that the Schottky Barrier FETChemFETs (32) may be similar in characteristics one to another.

FIG. 1N depicts a side sectional view of one example of thesemiconductor NW ChemFET (32) of FIG. 1K (section X-X), wherein theChemFET (32) is configured as a Junctionless FET. In this example thesemiconductor NW channel is uniformly doped in the sensing region (26)of the channel, in this case depicted as n doped (15). Source (22) anddrain (24) contacts are provided that contact the uniformly dopedsemiconductor channel forming a Junctionless FET and a gate (12) isformed over the channel region (26) and electrically isolated from thechannel by a gate dielectric (14). Because the semiconductor NW channelis uniformly doped in this example the semiconductor channelnanomaterial is relatively uniform and precise, so that the JunctionlessFET ChemFETs (32) may be similar in characteristics one to another.

FIG. 1O depicts a side sectional view of one example of thesemiconductor NW ChemFET (32) of FIG. 1K (section X-X), wherein theChemFET (32) is configured as a Tunnel FET. In this example thesemiconductor NW channel is doped so that an n doped semiconductorregion (15), an undoped semiconductor region (17) and a p dopedsemiconductor region (17) form a tunnel FET in the sensing region (26)of the channel. Source (22) and drain (24) contacts are provided thatcontact the channel and a gate (12) is formed over the channel region(26) and electrically isolated from the channel by a gate dielectric(14). Because the semiconductor NW width and cross-sectional area are sosmall it is difficult to dope the semiconductor channel nanomaterialuniformly and precisely, so that the Tunnel Junction ChemFETs (32) mayvary one to another. However, due to the way the Tunnel Junction ChemFETworks it has a lower subthreshold swing than the other examples andtherefore may offer lower power requirements for the sensor IC chip.

In various examples, as can be seen with respect to FIG. 1P, an analyteor reaction-sensitive layer (34), e.g., an oxide layer, can be disposedon the channel 30 and/or surface (21) and/or channel region (26), suchas layered or otherwise deposited or formed on the 1D or 2D nanomaterial(e.g., graphene) channel layer (30). Such an oxide layer (34) may be analuminum oxide, hafnium oxide or a tantalum oxide or any other oxidewith high intrinsic buffer capacity. In some examples, the oxide layermay have a thickness of about 30 nanometers, such as about 20nanometers, such as about 15 nanometers, such as 10, 9, 7, or 5nanometers or less. Particularly, the analyte and reaction-sensitivelayer (34), when present, may be composed of an inorganic material suchas aluminum oxide, hafnium oxide, tantalum oxide, or other insulating ornon-conductive material including organic materials such as polymers,and the like.

In various instances, as depicted in FIG. 1P, a passivation layer (36)may be disposed or otherwise be included on the surface (21) and/orchannel region (26) and/or oxide layer (34), such as layered orotherwise deposited on the 1D or 2D nanomaterial (e.g., graphene)channel layer (30) and/or on an associated analyte or reaction-sensitivelayer (34) on the surface and/or channel region (26). More particularly,the oxide layer (34) may have a suitable thickness such as of from about100 nm or about 75 nm to about 10 nm or 9 nm or less, such as about 0.5microns or about 0.1 microns or about 50 nanometers or less to about 20nanometers, such as about 15 nanometers, such as about 7 or about 5nanometers or less, respectively. Such a passivation layer may have athickness of about 5 microns or less, such as about 3 microns or about 1micron or about 0.5 microns. The thickness of the passivation layer ischosen in consideration of the fluid flow to the sensor chip and themethod of providing the ChemFET with targets or templates used fordetection. For example, the target or template may be affixed on amicrobead that in turn is located within a well or chamber of thepassivation material—in which case the polymer layer tends to thethicker end of the thickness range (e.g., 2 to 5 microns thick).Alternatively, if the targets or templates are affixed to the channel(30) or to an analyte or reaction-sensitive layer (36) on or over thechannel (30) then the passivation layer (36) can be thinner, such as 1micron thick or 0.5 micron thick or less, and only an opening isrequired in the passivation layer and not a well or chamber.

Once the appropriate electrode and channel structures have been formedproximate the dielectric insulating layer, a second insulation layer maythen be deposited over the dielectric, electrodes, and channel layers,which secondary insulating layer may also be patterned, such as byetching to form one or more chambers or wells, where the opening of thechamber and/or well corresponds to the formed channel region(s). Hence,in a manner such as this, the substrate may be configured so as toinclude one or more nano and/or micro chambers that may further beconfigured to form one or more sensing wells.

Accordingly, as presented with respect to FIG. 2A, a further aspect ofthe present disclosure is a biosensor (1). The biosensor includes asemiconductor structure (10) that may include a dielectric layer (20)having a metal layer containing a source (22), e.g., a damascene coppersource, as well as a metal layer containing a drain (24), e.g., adamascene copper drain, such as embedded within or on an insulatingand/or dielectric layer (20), e.g., positioned on top of the structure(10). The insulating layer may be an inorganic material, such as asilicon oxide, silicon carbide, or a silicon nitride, or mixturesthereof or an organic material, such as a polyimide, BCB, BPO or otherlike material. The biosensor may also include a 1D or 2D nanomateriallayered, e.g., a graphene layered, surface or channel (30) extendinghorizontally from the source (22) to the drain (24), so as to at leastbe proximate therewith and thereby form a sensing zone (26).

In this instance, the surface structure or channel (30) completelyoverlaps the source (22) and drain (24) regions. In other instances, thesurface structure or channel (30) partially overlaps the source (22) anddrain (24) regions. A further layer of passivation material (35) may bepositioned over the surface and/or channel (30), which layer of materialmay further be etched or otherwise configured to include a well orchamber structure (38) having a bottom surface that may be positioned onor proximate a portion of an exterior surface of the 1D or 2D or 3Dnanomaterial layer (30), such as to be coincident with the sensingregion (26). In such an instance, the well structure (38) may be alayered structure and may include a plurality of surfaces, such as first(39 a) and second (39 b) wall structures, such as extending from orotherwise being coincident with the surface (21) of the sensing zone(26). For instance, the wall structures (39 a, 39 b) may partiallyoverlap the surface structure (30).

Accordingly, FIG. 2A is an illustration of a ChemFET having agraphene-layered well structure (38), such as for a system for analysisof biological and/or chemical materials, reactions, or activity.

In particular instances, the well structure (38) may be configured so asto define an opening or chamber (37) that allows for direct contact withthe sensing surface (26), and thereby contact with the 1D nanomaterial,e.g., nanotube, nanowire, and/or 2D nanomaterial, e.g., graphene, layer(30). Hence, in various examples, the ChemFET device may be a cavitatedChemFET device, which may be configured so as to include a plurality ofwells or other chamber structures. In various instances, the ChemFETdevice (1) may be configured as a biosensor having a well structure (38)that further includes a passivation layer (35), as shown in FIG. 2B,which passivation layer (35) may be disposed in or on one or more of thechamber surfaces (30, 39). The semiconductor, e.g., CMOS, substratestructure (10) may additionally include the componentry typical of aCMOS semiconductor and/or transistor such as used and/or manufactured asan IC chip.

Hence, in certain instances, as illustrated in FIG. 2B, the ChemFET (1)may be configured as a chemically-sensitive transistor, and may beadapted to include one or more structures, such as nano- or micro-wells(38), that are formed as a sensing chamber, into which a fluid orsolution, e.g., a solution containing one or more reactants, may bedeposited, such as for the performance of one or more biochemicalsensings, such as a nucleic acid hybridization and/or sequencingsensing. In particular instances, the chamber (38) may include a sensingregion (26) having a 1D, 2D, or 3D nanomaterial channel (30), and/or oneor more analyte or reaction-sensitive layers (34) and/or passivationlayers (35) deposited therein or thereon. In such instances, the chamberof the ChemFET device may be configured as a solution gate and thereforethe ChemFET may be adapted so as to be an ISFET, such as configured forreceiving the reactants necessary for performing an analysis ofbiological and/or chemical materials, reactions, or biologic activity,for instance, a hybridization and/or sequencing reaction.

As can be seen with respect to FIGS. 2A, 2B, 3A and 3B, in variousexamples, a ChemFET (1) having a graphene layered well structure (38) isprovided. The ChemFET (1) includes a semiconductor substrate layer (10)and an insulating layer (20) within which is embedded the variousChemFET transistor components including a conductive source (22) andconductive drain (24) which may be adapted to form a channel sensingregion (26). In this instance, a graphene layer (30) is positioned overthe insulating layer (20) and positioned so as to contact at least aproximate portion of the source (22) and a proximate portion of thedrain (24) to form a channel (30). In this instance, the substrate layer(10) is composed of silicon, the insulating layer (20) is composed ofsilicon dioxide, and the source (22) and drain (24) are composed of aconductive metal, for example, as copper.

The source (22) and the drain (24) are separated from one another andpositioned relative to the graphene layer (30) so as to form a sensingregion (26). In this example, the sensing region (26) is further boundedby chamber walls (39 a, 39 b), which together form the well (38) intowhich a fluid may be delivered, such as for the performance of abio-chemical reaction, and thus, forming a solution gate configurationby way of a gate voltage applied by a gate or reference electrode (66).Particularly, a passivation layer (35), which may also be composed ofsilicon dioxide, may be positioned above the first silicon dioxide layer(20), and be configured, e.g., via etching, to form a well (38) so as toform a chamber (37), which chamber (37) may be adapted to receive asolution so as to form the solution gate region. The graphene layer (30)is disposed between the first (20) and second (35) silicon dioxidelayers such as to form the bottom surface of the chamber (37). In thisinstance, the ChemFET sensor is configured to detect a change in ionconcentration, e.g., pH, which occurs within the well (38) such as whena solution containing reactants is added to the sensor region (26)within the chamber (37), and the reactants interact with an additionalelement contained within the chamber, such as a bound nucleic acidtemplate.

Particularly, one or more solutions may be added to the chamber (37),such as in the performance of a bio-chemical reaction. For instance, afirst solution including a nano- or microbead (60) may be added to thewell (38). The nano- or microbead may be treated so as to be associatedwith one or more biopolymers, such as a DNA and/or RNA template (65).Once the nano- or microbead (60) containing solution is added to thewell (38), in such a manner that the bead (65) is retained therein, oneor more additional solutions containing reactants, such as for theperformance of a biological and/or chemical reaction, may then be addedto the well (38). For example, where the biological and/or chemicalreaction is a nucleic acid synthesis reaction (as occurs in NGSmethods), the analyte containing solution to be added to the well (38)may include a nucleotide and/or polymerase composition that if theconditions are suitable within the chamber (37) will result in a bindingand/or incorporation event occurring between the template molecule (65)and the nucleotide reactant, thus resulting in the reaction takingplace. Additionally, where the biological and/or chemical reaction is ahybridization reaction, the bound template molecule (65) may beconfigured as a probe, and the analyte containing solution to be addedto the well (38) may include an additional DNA/RNA molecule of interest,which if the conditions within the chamber (37) are suitable willhybridize to the bound probe, thus resulting in the reaction takingplace.

In either instance, the ChemFET (1) may be configured for detecting theoccurrence of a chemical reaction, such as by detecting a change in theionic concentration within the solution within the chamber (37).Particularly, if the conditions are suitable for a reaction to takeplace, e.g., the appropriate reactants are present, a binding and/orincorporation event will occur in such a manner that an ion, such as anH+ ion, will be released into solution, such as within the chamber (37)and/or proximate the sensing region (26). In such an instance, theChemFET (1) may be configured to sense the evolution of the ion,appreciate the change in pH, and detect that a reaction has taken place.In such a manner as this, a DNA/RNA molecule may be synthesized and/or ahybridization event determined.

Accordingly, as illustrated with respect to FIG. 3B, a ChemFET (1) isprovided wherein the transistor (1) includes a graphene layered wellstructure (38) containing a nano- or microbead (60) therein, such aswhere the graphene layer (30) may be coincident with a channel region(26) so as to form a sensing zone therewith. The ChemFET (1) mayadditionally include a passivation layer (35), in which is defined awell (38), including well sidewalls (39 a and 39 b). The ChemFET is alsoconfigured with a solution gate included of a fluid or solution (64) anda reference electrode or solution gate electrode (66). The microbead(60) may be included of targets or templates (62) to be analyzed.

For example, the microbead (60) may be covered with many copies of asingle stranded DNA template (62) such that when a complementarynucleotide binds to the DNA template a hydrogen ion (68) is released. Inthe case where the microbead (60) is covered with many copies of the DNAtemplate (62) then many hydrogen ions (68) may be released when multiplecopies of a nucleotide bind to the template DNA strands (68). TheChemFET (1) may sense the buildup of charge due to the release ofhydrogen ions thus transducing the chemical reaction of DNAhybridization to an electrical signal output by the ChemFET sensor.

Further, in various instances, such as illustrated in FIG. 3A, inaddition to a graphene layer (30), the channel region sensing zone (26)within the chamber (37) of the well (38) of the transistor (1) mayfurther include an analyte or reaction-sensitive layer (34), such as anoxide layer, associated with the graphene layer (30). Furthermore, ascan be seen with respect to FIG. 3B, in certain examples, the ChemFET(1) may include a plurality of nano- or microbeads (60) therein, such aswithin the chamber (37) of the well (38) of the ChemFET (1), so as toallow a plurality of reactions to take place at the same time involvinga plurality of microbeads (60 a, 60 b) within the well, which increasesthe surface area for reactions.

Improved Electrode to Channel Contact

As can be seen with respect to FIG. 2B, in particular examples, theprimary (10) and/or secondary (20) structures can be fabricated toinclude or otherwise be associated with a tertiary structure (35), suchas may be included of a non-conducting, insulating layer, such ascomposed of a silicon dioxide material. In various instances, thetertiary layer can be fabricated or otherwise configured so as toinclude a chamber or well assembly (38) in and/or on the surface (21),such as proximate the sensing zone (26). For instance, FIG. 2B depicts aChemFET (1) having a well structure (38), which well structure may bepositioned on a portion of a surface, e.g., an exterior surface (e.g.,21) of a primary (10) and/or secondary structure (20). In someinstances, the well structure (38) may have a plurality of walls orbounding members (39 a) and (39 b) set apart from each other by adistance that may (or may not) be equivalent to the space between thesource and drain so as to form the vertical boundaries of the chamber(38), with the bottom of the chamber forming the horizontal, bottomboundary.

In particular examples, the bottom of the chamber (38) may be configuredas a sensing zone so as to form a sensing region within the well (38).Particularly, the boundaries (39 a, 39 b) may be formed on top of, ormay otherwise include at least a portion of the 1D or 2D (e.g.,graphene) material (30), and/or may additionally include the sensing,e.g., oxide, and/or passivation layers (36). In various examples, thechamber and/or well structure (38) may define an opening (37), such asan opening that allows access, e.g., fluid access, to an interior of thechamber (38), thus allowing direct contact or intimate association withthe 1D (e.g., carbon nanotube or nanowire) or 2D (e.g., graphene)structure associated with the surface and/or channel region (26) and/oranother material layer associated therewith, e.g., (36).

Certain examples of ChemFETs can be fabricated in a manner to increasethe contact surface area between the source and drain and the materialused to form the channel. For example, a substrate can be provided,e.g., a silicon substrate. An insulating dielectric layer, e.g., anoxide layer, may then be deposited on the substrate, into which aplurality of materials may be deposited so as to form a channel regionwithin the dielectric layer. Thus, the dielectric layer may be processedin a manner of different ways, as set forth herein, so as to produce achannel, such as a channel comprising a 1D or 2D nanomaterial extendingbetween a plurality of electrodes, such as source and drain electrodes.Accordingly, once deposited and suitably positioned above the substratelayer, the dielectric layer may be subjected to further processing so asto form a channel region, the channel region being formed between twoopposed electrodes.

For instance, in an exemplary example depicted in FIG. 2B, the ChemFETmay be formed using the process steps outlined in FIG. 33. In this casethe channel material (30) is deposited or formed over the source (22)and drain (24) electrodes. It is important to insure good physical andelectrical contact between the channel material and the source and drainelectrodes. One method of insuring good contact is to have the electrode(22, 24) stand proud of the dielectric material (20).

In one instance, illustrated in the side sectional views of FIGS. 5A and5B, an electrode material (25) is located within trenches within thedielectric layer (20). If the electrode material is copper depositedthrough a damascene process, then it would be typical for a liner (67)to be provided on the trench sidewalls prior to the copper plating.Tantalum or tantalum nitride are two typical liner materials. In aparticular process step, as shown in FIG. 5A, the copper electrodematerial 25 is plated so as to fill the trenches and to overfill thetrenches and extend over the surface of the dielectric (20). In asubsequent process step, illustrated in FIG. 5B, Chemical MechanicalPolishing (CMP) is performed to remove the excess overplated coppermaterial and to planarize the top surface. The CMP process can beoptimized to reduce the height of the dielectric layer (20) so that itis below the height of the electrodes, essentially resulting inelectrode bumps (29) that protrude from the dielectric (20) surface.Protruding bumps are advantageous to insure good physical and electricalcontact between the channel material (30) and the electrode material(25).

In another example, as seen with respect to FIG. 5C, the processedand/or polished surface of an electrode may be further processed, suchas by being subjected to a plating process so as to add additionalconductive material to the contact region, e.g., to increase its heightabove the dielectric layer (20), to increase its surface area and/or togive the contact region of the electrode a desired shape orconfiguration prior to the deposition of the 1D or 2D nanomaterial layerthereon. Such plating may be performed in a variety of different ways,such as an electrolytic process and/or an electroless plating process,which allows the auto-catalytic plating on top of the depositedelectrodes, so as to further build up a configuration, e.g., a bump witha more pronounced offset above the dielectric layer. FIG. 5C showsplated bumps (29) on electrodes (25) that extend above the surface (21)of the oxide layer (20).

In various instances, once formed, the electrodes (22, 24) may then becontacted with a 1D and/or 2D channel forming material in such a mannerthat a channel (30) forms between the first and second electrodes, thatis between the source and drain electrodes. In certain instances, thelayering or otherwise depositing of the 1D or 2D nanomaterial over thechannel area (26), so as to form the channel (30) between the source(22) and drain (24) electrodes, is performed in such a manner so as toincrease the surface area of one or more edges of the channelnanomaterial coming into contact with the electrode material. This isuseful because carrier mobility may be increased through the interfaceof the electrode and the channel member at these one or more edges.Hence, it has been discovered that increasing contact efficiencyincreases carrier mobility through the channel (30). Accordingly,presented herein are field effect transistors that have optimalchannel/electrode interfaces that maximize this contact.

For instance, as described herein above, the 1D or 2D nanomaterial layerpositioned between the electrodes can be arranged in such a manner thatonly a bottom surface of the 1D or 2D nanomaterial contacts theelectrode surface, e.g., a bottom side contact. However, in someexamples, the configuration of the contact area may be configured suchthat as the 1D or 2D nanomaterial contacts the electrode material itdoes so in a manner so as to form an edged interface, which edgeconfiguration may be particularly useful in increasing the flowefficiency of carriers through the channel. Further, this contact regionmay additionally be configured to include one or more of a bottom sidecontact, an edge side contact, a top-side contact, as well as multipleedge contacts, and interior and exterior side or edge contacts.

In various instances, such as those shown with respect to FIGS. 5D and5E, the graphene and/or electrode layers may be additionally configuredto further increase the relevant surface area of the contact. Forinstance, once the graphene layer (30) has been deposited, one or moreopenings (31) or holes, vias, or trenches may be made into the channelmaterial layer over source and drain electrode locations, which then maybe subjected to another plating process to further build a metal contactsurface with the graphene layer (30), thereby increasing contact betweenthe graphene layer (30) and the electrode layer (22). In this respectcontact is provided not only at the bottom surface of the channelmaterial, but also on edge surfaces within the holes, and on the topsurface of the channel material where the bumps (29) extend horizontallybeyond the hole dimension to overlap onto the channel surface.

Accordingly, in various instances, a hole may be made through thegraphene layer to the underlying metal layer of the electrode, whichhole may then be filled with a secondary metal material, which materialmay be the same or different metal as the electrode, and thus anenlarged surface area contact is formed, as illustrated by FIGS. 5D and5E. In some examples, the electrode material may come up through thebottom of the holes to cover at least a portion of the top of thetransistor material, e.g., graphene, layer; or metal may be plated ontop of the graphene layer and travel downwards into the holes therebycontacting the electrode metal layer thereunder.

Accordingly, in various examples, once the electrodes have beenfashioned and/or the 1D or 2D channel formed in conjunction therewith,e.g., such that the channel nanomaterial extends between the source anddrain electrodes, one or more of the contact regions between the channelnanomaterial and that of the electrode material may be furtherprocessed. For instance, the contact area of the channel nanomaterial(30) may be patterned, e.g., one or more openings (31a, 31b, 31 c) maybe made in the channel and other associated material layers, to enlargean additional surface area, and a second metal portion or cover (29) maybe deposited into the openings, thereby creating a further contactinterface between the metal electrode material (25) and the channelnanomaterial (30).

The second metal portion may extend vertically above the surface of the2D nanomaterials, as well as laterally on top of the 2D nanomaterial adistance that is greater than the diameter of each opening. The shape ofthe openings in the channel material (30) may have any suitableconfiguration such as round, elliptical, square, rectangular,rhomboidal, and the like, so as to maximize the effective contact area.Hence, in such a configuration, the contact area between the channelnanomaterial and the electrode material may include one or more of abottom contact area, an outside contact area, an inside contact area,and/or a top contact area. Thus, once the 1D or 2D nanomaterial layer isapplied over the electrode layer of the dielectric layer, the 1D or 2Dnanomaterial may be patterned, so as to create an opening in the contactregion, which opening may then be filled with another metal materiallayer, such as copper, nickel, platinum, palladium, and the like, whichsecond metal layer may then be patterned as well, if desired.

Particularly, once the electrode area and 1D/2D nanomaterial interfacehas been formed in the desired configuration, then, if desired, thesurface thereof may be patterned. For instance, once the 1D/2Dnanomaterial, e.g., graphene, is laid down, a photo-resist and/or maskhaving the desired configured cutouts may be placed over the channelregion and/or graphene, such as where the pattern includes protectedregions where patterning, e.g., etching, is not desired. Once suitablyprotected where desired, then an etching process, e.g., a dry or wetetching process may be employed so as etch the surface of the 1D or 2Dnanomaterial and/or channel region into the desired pattern where the 1Dor 2D nanomaterial layer is not protected.

In some examples, multiple openings or holes may be used to connect 1D,2D nanomaterial channels (30) to electrodes. FIG. 5F illustrates aChemFET (1) wherein the practices just described for forming conductivematerial through holes in the channel (30) to increase contact area withthe electrodes (22 and 24) is practiced. In this example the addedmaterial that forms the bumps (29) projects through multiple holes inthe channel (30)—some holes over the source electrode (22) and some overthe drain electrode (24).

In the example shown in FIG. 5F, an ion sensitive layer (34) ispositioned over the 2D nanomaterial (30). Multiple holes or openingshave been patterned through the 2D nanomaterial (30) and ion sensitivelayer (34). Conductive covers or deposits or bumps (20) are positionedproximate respective electrodes (22, 24) and contact respectiveelectrodes (22, 24) through openings in the 2D nanomaterial (30) and ionsensitive layer (34). In some examples, the electrodes (22, 24) may bepositioned in trenches created in an insulating dielectric layer (20),as described above. As depicted, in various examples, the ChemFETnanomaterial transistor connects to a respective drain or source of asemiconductor access transistor (11) positioned at least partially in asubstrate layer (10), e.g., a silicon semiconductor. A gate (13) allowscontrol of the semiconductor access transistor (11).

Biologic and Analyte Detection with a ChemFET

In some examples, the ChemFET may include a plurality of wells and aplurality of ChemFETs may be configured as an array, e.g., a sensorarray IC chip. It may be noted that having multiple wells sensing thesame analyte or reaction allows statistical improvement of the sensingresult. Such a ChemFET sensor IC chip is shown in FIGS. 15A and 15B andmay be employed such as to detect a presence and/or concentration changeof various analyte types in a wide variety of chemical and/or biologicalprocesses, including nucleic acid hybridization (e.g., DNA/DNA, DNA/RNA)and/or DNA or RNA sequencing reactions. For instance, the devices hereindescribed and/or systems including the same may be employed in a methodfor the analysis of biological or chemical materials, such as for wholegenome analysis, genome typing analysis, microarray analysis, panelsanalysis, exome analysis, microbial/microbiome analysis, genotypinganalysis, and/or clinical analysis, such as cancer analysis, NIPTanalysis, cfDNA, blood/plasma/serum analysis, UCS (upstream conservedsequence) analysis, biomolecule analysis and/or analyte analysis.

In a particular example, one or more surfaces within the wells (38) ofthe ChemFET (1) may be configured as a sensing zone, which sensing zonemay include an additional structure, such as a 1D, 2D, e.g., graphene,or 3D material layer, and hence, the FET may be a graphene FET (gFET).There are several ways in which an analyte or biologic material orreagent may interact with the ChemFET.

In one instance, illustrated in FIG. 3B, a microbead (60) is used tohold reagents, such as single-stranded DNA templates. The microbead (60)with its DNA templates (82) is introduced into the chamber (37) of thewell (38). A fluid (64) may deliver additional reagents to the well(38). The ChemFET (1) senses changes in the electric field due to thepresence of the reagents or due to chemical reactions occurring amongthe reagents. For example, incorporation of a nucleotide base onto atemplate DNA strand will release hydrogen ion. When many (thousands ormore) of the templates are on a microbead then thousands or morehydrogen ions will be released during the base incorporation. Thesecharges may be sensed by the ChemFET (1). Use of a microbead withtemplates may be particularly suited to DNA or RNA sequencing.

In another instance, illustrated in FIG. 3C, the templates are attachedto the sensor surfaces, such as to the bottom of the well (38) or thesidewalls (39) of the well (38). Depending on the configuration of theChemFET, the attachment may be to an analyte or reaction-sensitive layer(34) over the channel (30) or may be directly to the channel material(30). This configuration can be used for DNA or RNA sequencing amongother uses.

In a further example, shown in FIG. 3D, antibodies may be attached tosurfaces of the sensor, such as to an analyte or reaction-sensitivelayer (34). In this case the binding of antigens to the antibodies maybe sensed by the ChemFET.

In yet another example, shown in FIG. 3E, a cell or other biologicstructure or material may be located in the well (38) of the ChemFET(1). Activity of the biologic material or reaction of the biologicmaterial to components within the fluid (64) may be sensed by theChemFET.

The ChemFET, e.g., a well or chamber thereof, may be configured forchemical or biological material detection, chemical reaction detectionor biologic activity detection, such as where the biological materialmay include one or more biological polymers, nucleic acids, such as DNAor RNA, proteins, carbohydrates, lipids, cells, virus particles,antibodies, peptides, polysaccharides, ions associated withbiomolecules, and the like.

These are but a few examples of methods to interface an analyte orbiologic material with the ChemFET.

ChemFET Analyte or Reaction Sensitive Layer

Another aspect of the present disclosure is the inclusion of an analyteor reaction-sensitive layer, such as an ion sensitive layer, to thechannel to improve the sensitivity of the 1D or 2D nanomaterial channelof the ChemFET.

In particular instances, a sensing layer can also be provided, such as alayer associated with the 1D or 2D nanomaterial, e.g., graphene layer or3D structural layer. For instance, in one example, a thin (0.01 micron)etch stop layer (ESL) may be placed over the channel layer (e.g.,graphene), such as in the case where a well etch process affects thechannel-forming material. In various examples, an oxide layer can beincluded, such as disposed within the well, chamber and/or channelthereof. Particularly, in various examples, a method for depositing thedielectric layer may include Atomic Layer Deposition (ALD).

In the case of graphene and other 2D nanomaterials they may have fewdangling bonds and therefore it may be difficult to get an initialdeposition of a sensing layer to stick or adhere to the nanomaterial. Insuch cases a preconditioning of the nanomaterial may be required priorto the preferred dielectric deposition process of ALD. Such preconditionmay include, but is not limited to plasma or ozone treatments, polymerfunctionalization (especially with thin SAMs), chemical bondfunctionalization (e.g., replacing some of the carbon atoms in thegraphene with fluorine, chlorine, or other species), or low temperatureand long cycle ALD prior to normal ALD processing.

Another method for creating an analyte or reaction-sensitive layer is tofirst deposit a metal layer (e.g., by sputtering or evaporation) ontothe 1D, 2D, or 3D nanomaterial layer and then oxidizing the metal toform a metal oxide layer. It is further possible to combine materiallayers using different deposition processes to create an analyte orreaction-sensitive layer. For example, a first layer can be included ofsputtered metal that is oxidized, followed by a layer included of an ALDdeposited oxide. It is further possible to combine two or more analyteor reaction-sensitive layers, such as may be included of differentmaterials to create an overall analyte or reaction-sensitive layerstack. For example, a first layer of metal, e.g., aluminum oxide, may beformed over the channel nanomaterial and then a second layer of metal,e.g., tantalum oxide, can be formed over the aluminum oxide. In someexamples, an analyte or reaction-sensitive dielectric layer need not berequired nor used.

However, where employed, the oxide or other sensing layer may beconfigured so as to prevent the nucleic acid template or probe, e.g.,present on a microbead, from contacting the 1D or 2D nanomaterial orother sensing layer of the chamber directly. The oxide layer can becomposed of an aluminum oxide, tantalum oxide, and/or a hafnium oxide.In various instances, the oxide layer may have a thickness of about 30nm, such as about 15 nm, such as 9 nanometers or less. In furtherinstances, the ChemFET can read through an oxide layer, if present.

ChemFET with Two Sensing Layers

Additionally, as shown in FIG. 3F one or more additional analyte orreaction-sensitive layers (34, 61) can be included in the ChemFET, suchas formed on the sidewalls (39) and bottom (21) of the well (38). Forinstance, FIG. 3F depicts a cut-away view of a substrate (10), whereinthe substrate includes a well (38) having a chamber therein, such as achamber defined by one or more walls. In various instances, one or moreof the walls may have a second analyte or reaction-sensitive layer (61)coating the walls (39) of the well (38). Particularly, a substrate (10)may be provided such as where the substrate (10) may be formed of asilicon layer and may include one or more additional layers, such as oneor more dielectric layers (20) and a passivation layer (35), whichlayers may be composed of silicon dioxide. Imbedded within one or moreof these layers may be a pair of electrodes, such as a source electrode(22) and a drain electrode (24), which may be in one or more of theconfigurations set forth in FIG. 5G, or another suitable configuration.As can be seen, one or more of the dielectric layers (20) and/orpassivation layer (35) may be configured so as to include a wellstructure (38), which structure may further be adapted so as to includeone or more additional layers (61), such as a plurality of analyte orreaction-sensitive layers (34, 61). For instance, one of the analytesensitive layers (34) may be positioned on a bottom surface (21) of thewell (38), such as layered upon a channel member (30), such as upon agraphene channel layer (30). Additionally, another analyte sensitivelayer (61) may be layered upon one or more of the well-bounding members(39 a, 39 b).

ChemFET Channel Enhancements Interdigitated Source and Drain Channelwith High W/L Ratio

Accordingly, in one aspect of the present disclosure, the sensor isconfigured as a ChemFET. Particularly, in certain examples, the ChemFETincludes a chamber having a channel structure incorporated or associatedtherein. In particular examples, the chamber and/or the channel and/or astructure thereof is optimized in such a manner so as to maximize theratio of channel width (W) to channel length (L). For instance, thechannel may include a 1D or 2D or 3D structure, such as where thechannel and/or the channel structure includes a geometry that has beenoptimized to maximize the ratio of channel width (W) to channel length(L). This can be accomplished, for example, through the use ofinterdigitated source and drain electrode geometries in a single planeor through the use of 2D and/or 3D electrode structures, such as a 3Dinterdigitated well structure.

In such examples, the transistor includes a channel extending between,or spanning, a conductive source and a conductive drain to form thechannel structure. In such examples, the opening of the chamber ispositioned in relation to the channel so that the opening aligns withthe source and drain, and more particularly, with the associatedchannel. As indicated, in various examples, a channel of the ChemFETincludes a one-dimensional (1D) transistor nanomaterial (e.g., a carbonnanotube (CNT) or a semiconductor nanowire) or a two-dimensional (2D)transistor nanomaterial, such as composed of graphene, molybdenumdisulfide, other metal dichalcogenides, and black phosphorous. Invarious instances, a three-dimensional (3D) structure may be included.

For example, the transconductance through the channel may be modified invarious manners so as to modulate, e.g., increase, the sensitivity ofthe associated ChemFETs, such as in the sensor array. Particularly, invarious instances, it may be useful to configure the chamber and/or wellso as to have a short channel length and a wide channel width, such asthe shortest channel length and largest channel width possible, giventhe configuration of the one or more chambers in the one or more sensorarrays. More particularly, an equation for transconductance of the FETsdisclosed herein is: g_(m) ∝ μC_(ov) W/L Vsd where g_(m) is thetransconductance, μ is the carrier mobility, C_(ov) is the overallcapacitance of an included oxide or other layers over the transistor, Wis the channel width, L is the channel length and Vsd is the voltagefrom the source to the drain. Since gm directly relates to thesensitivity of the sensor it is desirable to increase gm through theterms shown in the equation. In particular, increasing the W/L ratio(maximizing W and minimizing L) will increase gm.

In particular instances, the length of the channel from the source tothe drain ranges, and in some instances, may be less than about (1)micron, such as less than about 500 nm, including less than about 50 nm,and in particular instances: as short as the fabrication process willallow without generating defects or results that render the deviceunusable. In one particular example the channel length is about (20) nmor less. Conversely, the width of the channel may be as wide as feasibleand/or possible. In such an instance as this, the width of the channelneed not be governed by the fabrication process as much as by the designrequirements of the overall sensor chip. For instance, in specificinstances, hundreds of thousands to millions of sensors may be includedin an exemplary sensor chip.

However, with such a large number of sensors, each individual sensorsize and/or pitch, e.g., which may directly affect the channel width,should be kept reasonably small so as to prevent the chip from being solarge as to be unable to be fabricated (e.g., such as exceeding thephotolithography reticle size) or too expensive (e.g., due to the effectof defect density on a large chip size). Hence, in one implementation,e.g., of a rectangular channel design, a practical range of the channelwidth is from about 0.1 micron to about 10 microns, such as from about0.1 to 5 microns. As indicated above, in some instances, it may bedesirable to increase the channel length to channel width ratio, such asthrough the use of various design techniques. In one particularexemplary instance, a structure, such as an interdigitated tooth andcomb structure, can be provided such as for short channel lengths andlarge channel widths, such as within a relatively compact area, such asshown in FIG. 1I, which depicts various planar structure designs ofinterdigitated source and drain electrodes that can be implemented so asto increase the W/L of the channel within a relatively small area.

Further, with respect to FIG. 5H as previously noted, in variousinstances, it may be desirable to increase the ratio of the channelwidth W to the channel length L (e.g., W/L). For instance, FIG. 14depicts a FET device, as herein described, wherein the FET includes awell having one or more walls that may be configured to produce orotherwise include a 3D interdigitated electrode. Particularly, having awell structure, as set forth in FIGS. 12 and 13, allows the formation ofsource (22) and drain (24) electrodes not only on the bottom of the well(21), but also may be fabricated on the sides of the well (39), such asin one or more of the configurations set forth in FIG. 5G.

Specifically, FIG. 5H depicts a well structure in a cross-section viewthat has one or more surfaces that have been configured for allowing oneor more electrodes to be fabricated therein. In this instance, thesource electrodes (22) and drain electrodes (24) are interdigitated andpositioned both on the bottom (21) of the well and on the sides 39 ofthe well. Many geometric patterns can be designed for source (22) anddrain (24) electrodes to cover both the sides and bottom of the wellsand the pattern shown in FIG. 14) is but one example, while FIG. 5I isanother example, such as where the well includes a transistor materialor an analyte or reaction-sensitive layer that may be positioned orotherwise coated over the surface of the well bounding member and/or oneor more electrodes configured therein.

For example, one possibility for forming the source (22) and drain (24)electrodes in the well (38), such as in a 3D structure as set forthherein, is to use a photopatterning or photolithographic process. Insuch an instance, a mask with the desired pattern(s) may be used totransfer a pattern onto a photosensitive photoresist material. Thepattern in the photoresist material can be used to likewise define apattern in the conductive electrodes (e.g., by etching, lift-off,plating, and/or other processes known in the art). For instance, it ispossible by employing the right optics to expose photoresist into deeptrenches and/or wells so as to be able to define conductive traces inthose deep trenches or wells. An example of this is shown in FIG. 16,which presents a depiction of an interdigitated well structure that hasbeen fabricated using lithographic methods. Other techniques that canaddress patterning of photoresist in deep trenches or wells are laser,electron beam, and/or plasma, and the like.

Particularly, in various instances, once the source (22) and drain (24)electrodes are formed on the sides (39) of the well (38) the channel(24) may be formed over the electrodes. The process used to form thetransistor channel (24) may be by any suitable process, but may dependon the materials being deposited and the presence of process limitsimposed by other devices incorporated into the sensor. For instance, asilicon-based CMOS wafer with conventional transistors (e.g., formedfrom doped regions in the silicon and polysilicon or metal gates) willtypically have a processing temperature limit of 350 to 400 C, abovewhich damage to those transistors may occur. So, for a CMOS wafer withadded sensors, the deposition of the materials making up those sensorswill typically be lower than 400 C, which can be accomplished either bya low-temperature in-situ deposition processes, and/or by creating thedesired sensor materials separately and transferring them to theappropriate locations on the CMOS wafer.

In some instances, a 1D or 2D transistor material (30) can be formedseparate from the CMOS wafer and then be transferred onto the electrodestructures in the wells (38), as shown in FIG. 5I In another instance,another option may be to deposit a transistor channel nanomaterial onthe electrodes (22, 24) and well walls (21, 39). This may beaccomplished by low temperature (e.g., below 400 degrees C.) depositionof amorphous silicon or suitable 2D nanomaterial by any suitable meansincluding, but not limited to: CVD, ALD, PVD (e.g., evaporation and/orsputtering), PECVD, and/or the like. Likewise, as depicted in FIG. 5I,one or more of these methods can be used to coat the interior chamber ofthe well structure with a transistor material, such as an analyte orreaction-sensitive layer.

Additionally, FIG. 5K depicts an alternate well structure (1). In thisinstance grooves or trenches 61 may be formed in the wall boundaries ofthe well 39. These grooves 61 can help to align and capture the 1Dand/or 2D transistor channel nanomaterial—such as carbon nanotubes orsilicon wires. Accordingly, FIG. 5K depicts a well that uses carbonnanotubes to create interdigitated transistors, such as in a verticaldirection.

Vertically Interdigitated and Stacked 3D Source and Drain

FIG. 5L depicts a top-plane view of a geometric pattern of source (22)and drain (24) electrodes that might be found at the bottom (21) of thewell structure (38) shown in cross-section view in FIG. 5M. FIG. 5Lshows an alternating pattern of source (22) and drain (24) electrodes atthe bottom of the well structure (38), in this case in the form ofconcentric ring shapes embedded in the dielectric layer (20). In afashion similar to the previously discussed interdigitated source anddrain designs, the channel W/L ratio for concentric source and drainelectrode rings can be high—especially if the distance between the ringsis small. The channel (30) will later be formed over the source (22) anddrain (24) by the deposition of the channel nanomaterial (30) over thesource (22) and drain (24).

For instance, FIG. 5M depicts the use of the bottom source (22) anddrain (24) electrodes as shown in FIG. 5L as well as the use ofalternating vertical metal source (22) and drain (24) electrode layers,which may be positioned, such as within a chamber (37) or the boundingmember(s) (39) defining the chamber, so as to create an interdigitatedtype of effect in the vertical direction and thereby maximize the ofratio channel width W to channel length L, as herein described.Particularly, FIGS. 27 and 28 depict a ChemFET (1) included of adielectric material (20 and/or 35), and having a chamber (38) formedtherein, such as by etching.

The chamber (38) includes a wall (39) and/or a bottom surface (21)having a plurality of electrodes disposed therein, such as a sourceelectrode (22) and a drain electrode (24), such as where the electrodeshave been configured in an interdigitated manner both in a horizontaldirection at the bottom (21) of the chamber (37) and in a verticaldirection along the height of the chamber (37). It is to be noted thatalthough a particular electrode configuration has been depicted, anysuitable configuration can be implemented, such as those depicted inFIG. 5G.

To demonstrate the desirability of forming 3D electrode structures onthe well surfaces (39 and/or 21), a comparison of the ratio of channelwidth to channel length (W/L) can be made of a device that only haselectrodes (22) and (24) on the well bottom (21) versus one withelectrodes on the well bottom (21) and well walls (39). For instance,with respect to the well structure depicted in FIGS. 5L and 5M, e.g.,with a nominal 1 micron well diameter (at the well bottom (21)), thechannel length of channels (24) either at the well bottom (21) or on thewell walls (39) is 100 nm, for example. For the well bottom (21), thechannel (24) width is given by the formula 2πR (it is thecircumferential distance of the channel defined by the gap between thesource (22) and drain (24) electrodes). If one assumes the radius of thechannel (24) is 150 nm, then the channel width is about 945 nm. Thisresults in a W/L of about 9.45. Further, as depicted in FIGS. 27 and 28,there are multiple electrode layers, such as in a vertically stackedconfiguration that circumscribes and/or surrounds the well opening (37).In such an instance, the channel length may be about 100 nm. In thisinstance the channel width is contributed by the circular gap betweeneach electrode layer times the number of such gaps.

For example, for 6 gaps, where the well diameter is 1000 nm, the channelwidth due to the sidewall structures is: Wvertical=2πN=6.3×500 nm×numberof levels=3150 nm×6=18900 nm. Further, if the channel width at the wellbottom is added, a total channel width is 19845 nm and a W/L of 198.This is more than a (20) times higher W/L than the case with anelectrode structure only on the well bottom. As described above, theelectrode structures (22), (24) on the well sidewalls (39) and at thewell bottom (21) may be covered by a transistor channel nanomaterial(30), such as depicted in FIG. 5N Furthermore, an analyte orreaction-sensitive layer (34) (not shown) may be deposited over thechannel nanomaterial (30) on the well boundary walls (39) and bottom(21). Particularly, FIG. 5N depicts a well chamber (38), wherein thechamber (18) may be configured to include a transistor channelnanomaterial (30) and optionally an analyte or reaction-sensitive layer(30) (not shown).

In various instances, the source (22) and drain (24) electrodes can formelectrode pairs that are separated one from the other by a distance suchas to from an interdigitated source (22) and drain (24) electrode pair.As presented in FIG. 6A, the source (22) and drain (24) electrode pairsmay be configured so as to form a channel between the two electrodes,such as in the space between the two electrodes. In such instances, asdepicted in FIG. 6A, the channel may be included of or otherwise containa 1D or 2D channel nanomaterial (30), such as a carbon nanotube and/orgraphene layer. Hence, an option for forming one or more channels (24)with small lengths and high effective widths is to vertically alternatenot only the source (22) and drain (24) electrode layers, but also thetransistor channel nanomaterial (30) (e.g., 1D or 2D nanomaterial)layers, as depicted in the well structure (38) cross-section as shownFIG. 6A. In this case, the channel nanomaterial (30), e.g., a series ofgraphene layers, is interspersed between source (22) and drain (24)electrode layers. Hence, performing the same calculation as before, butin this case using a channel length of 0.345 nm (the thickness of asingle layer of graphene is 0.345 nm) results in a W/L ratio of 57,522which is more than 290 times higher than the previous calculation anddemonstrates the effectiveness of using thin channel nanomaterial layers(30) stacked vertically in an alternating fashion with the source (22)and drain (24) electrodes as part of the device structure.

FIGS. 6B-6I depict one implementation of a process flow that may beemployed to form the source (22) and drain (24) electrode layers as wellas the 1D or 2D channel nanomaterial layer (30). For instance, FIG. 6Bdepicts the bottom (21) of a substrate or well that may be configured soas to include a conductive source (22) and drain (24) electrodes. Thesemay, for example, be fabricated and/or formed by various fabricationprocesses as herein described and/or known in the art, such as by usinga damascene metal process.

The surface of the device may be Chemically Mechanically Polished(CMP'ed), such as after the conductive source (22) and drain (24)electrodes are formed in the well bottom (21). It is to be noted, thatFIG. 6B depicts the conductive source electrode (22) and conductivedrain electrode (24) at any given level or layer of the device, whereelectrodes are formed, the electrodes can be formed of the same materialduring the same process step or different. For example, the source (22)and drain (24) electrodes of FIG. 6B could be included primarily ofcopper that is deposited by an electroplating process with both types ofelectrodes formed in the same process step and in the same materiallayer.

FIG. 6C depicts a layer of a 1D or 2D channel nanomaterial (30) that hasbeen deposited over the electrodes in the well bottom (21). The channelnanomaterial (30) may be patterned so that it just covers all of theunderlying conductive electrode pattern or it may be sized smaller orlarger than the underlying electrode pattern—as long as it overlaps witha portion of the electrodes.

The next step, shown in FIG. 6D, is the deposition of an insulatinglayer (35) and then the formation of a trench (31) in that layer. Atsome locations in the trench the underlying channel material (30) isexposed.

FIG. 6E shows the trench being filled by conductive electrode materialto form a source (22) and drain (24) electrode on that layer. Duringthis step vertical electrode connections, e.g., vias, may be formedoutside of the electrode patterns. Such vias may be stacked layer bylayer as the process progresses allowing the vertical interconnection ofsource electrodes (22) on different layers, and allowing the verticalinterconnection of drain electrodes (24) on different layers.

These process steps may be repeated in FIGS. 6F, 6G and 6H to createvertical layers of alternating source electrode (22), transistor channelnanomaterial (30), and drain electrode (24), such as in a verticalinterdigitated configuration, as herein described. Duplicating thesesteps for further repetitions allows higher numbers of alternatingsource electrode (22), transistor channel nanomaterial (30), and drainelectrode (24) layers to be formed.

When the selected number of layers have been formed the central portionof the well (38) can be etched (e.g., by plasma, RIE, DRIE or a similarprocess) as to result in a ChemFET (1) with a well structure (38) andchamber (37) as shown in FIG. 61. This results in the fully formed layerstack depicted in FIG. 6A, wherein the chamber (37) provides access tothe ChemFET transistor for sensing. In this example the ChemFETtransistor has multiple channels (31) in parallel due to the verticallystacked and interdigitated source (22), channel (30) and drain (24)structure herein described.

Furthermore, since in many applications a fluid will be introduced inthe chamber (37) for the purpose of supplying a gate voltage (solutiongate) and/or reactants for a chemical reaction to be contained withinthe chamber (37) it is necessary to cover the exposed source (22) anddrain (24) electrodes with an insulating layer so that they are notelectrically shorted by the fluid. In one instance an analyte orreaction-sensitive material (24) can be deposited or formed to cover thechamber (37) sidewalls (39) and thus covering the exposed portions ofthe source (22) and drain (24) electrodes as well as the exposedportions of the channel nanomaterial layers (30). In this example, notonly does the analyte or reaction-sensitive layer (34) insulate theelectrodes (22, 24) from the fluid, but also the layer (34) may improvethe sensitivity of the ChemFET (1) due to the material's sensitivity tocertain analytes or reaction products, such as hydrogen ions.

FIGS. 6J and 6K depict a different example for forming alternatinglayers of electrodes (22, 24) and transistor channel nanomaterial (30).In this case vias, e.g., through-holes, trenches, and/or slots (31) maybe formed in the transistor channel nanomaterial (30) as shown in FIG.6K. In a subsequent step (not shown in the figures) the formation of theelectrode material (22 or 24) over or on the patterned channelnanomaterial (30) will also fill these vias. This allows not only asurface area connection from the electrode (22, 24) to the channelnanomaterial (30) but also an edge connection to the channelnanomaterial (30) (e.g., in the via the electrode material (22, 24) maycontact the edge of the channel nanomaterial (30)). In some materials,such as graphene, it is known that edge connections from electrodes (22,24) to the graphene channel nanomaterial (30) may result in lowercontact resistance between the two materials and better transistorperformance.

Accordingly, in various aspects of the disclosure, achemically-sensitive field effect transistor (FET) having amulti-layered structure is provided. For instance, the ChemFET mayinclude a first layer such as a substrate layer. The substrate layer,like all layers described herein, may have an extended body including aproximal portion having a proximal end, a distal portion having a distalend, and a pair of opposed side portions, all of which together define acircumference for the substrate layer. Additionally, a second layer,e.g., a first non-conductive material layer, may be included wherein thefirst non-conductive material layer may be a dielectric layer and bepositioned above the extended body of the substrate layer. In variousexamples, a second non-conductive material layer, which may also be adielectric layer, may also be included and positioned above the firstnon-conductive dielectric material layer.

In various examples, one or more conductive elements (e.g., composed ofan electrically conductive material), such as one or more electrodes,such as a source electrode and a drain electrode for a transistor, maybe provided. In various instances, the conductive elements may beseparated one from the other and positioned within one or more of thenon-conductive layers so as to from a channel between the electrodes. Inparticular examples, the source and drain electrodes may have a planararrangement and may be in an opposed configuration to one another, whereone or both of the source and drain electrodes have a geometricalformation or pattern designed to maximize the ratio of the channel widthto channel length. For instance, the source and drain electrodes may beconfigured, e.g., within the insulating layer such that the channellength is less than about 1000 nm, less than about 500 nm, less thanabout 100 nm, may be less than about 50 nm, or may be less than about(10) nm, less than about 5 or 3 nm or less.

Further, in various examples, the ChemFET may include a well structure,provided at least within the first and/or second non-conductive materiallayers. In such an instance, the well structure may include a chamber,such as a chamber that may be bounded by one or more bounding members.For instance, the bounding member may be configured as a plurality ofwalls or a circular circumferential surface member. In particularexamples, the bounding member(s) and/or the surrounding insulatinglayer(s) may be configured to include the source and drain electrodes.

For example, one or more, e.g., both of the source and drain electrodesmay be configured so as to be included within a bottom and/or a sidesurface on the well bounding member. In such an instance, the source anddrain electrodes may be configured so as to increase the channel widthto length ratio. Particularly, the source and drain electrodes may havea three-dimensional (3D) configuration and may be incorporated on orwithin the bottom surface member of the chamber and/or be incorporatedwithin one or more side or circumferential surface members of thechamber. In such instances, the source and drain electrodes may beconfigured so as to increase the channel width to length ratio by afactor of about 10 or 20 or more, e.g., compared to an electrode patternonly at the bottom of the well, such as by a factor of 100 or more, suchas a geometric electrode pattern that increases the channel width tolength ratio by a factor of 1000 or more.

Particularly, in certain examples, the source and drain electrodes maybe separated one from the other by one or more spaces, and thus, may beconfigured to not only have a 3D structure but to also be in an opposedbut interdigitated relationship to one another. For instance, one ormore of the source and drain electrodes may be formed so as to includean impingement member, and one or more of the source and drainelectrodes may be formed so as to include a receiving member, such aswhere the impingement member is configured for being inserted within thereceiving member, and the receiving member is configured for receivingthe impingement member, while maintaining a distance between oneanother, such as to form one or more channels there between.

Hence, in various instances, the source and drain electrodes may haveone or more, e.g., a plurality of, prongs or tines so as to give theelectrode a fork like configuration, such as can be seen with respect toFIG. 5G, where the tines are capable of being fit one within the otherwhile maintaining a space there between. In such instances, theinterdigitated tines of the source and drain electrodes may be disposedwithin one or both of the first and second non-conductive materiallayers and be separated from one another by a distance so as to form thechannel.

In particular examples, the bounding member(s) of the chamber may beconfigured so as to include one or more vias, trenches, or slots thatmay be formed in the transistor channel nanomaterial, which may then befilled with the electrode material so as to allow the formed electrodesto not only contact the well surface, but to also be in contact with thechannel and/or a material layer designed to form or otherwise augmentthe channel conductivity. Accordingly, in various examples, a channelnanomaterial layer may be provided, and the source and/or drainelectrodes may be configured so as to contact the channel nanomaterialand/or to also contact an edge of the channel nanomaterial.

Thus, in various examples, the chemically sensitive FET may beconfigured to include a channel, such as a channel that includes or isotherwise composed of a transistor channel nanomaterial, such as isformed over and/or between the electrodes, e.g., the source and drainelectrodes. For instance, a 1D, 2D, e.g., a graphene layer, and/or 3Dstructured layer, may be positioned between the first and secondnon-conductive material layers. For example, the transistor materialchannel nanomaterial may be a 1D nanomaterial may be included of carbonnanotubes or semiconducting material such as in a nanowire form, such asincluding Si, Ge, or a metal oxide.

In other instances, the 2D nanomaterial may be composed of one or moreof graphene, molybdenum disulfide (MoS2), MoSe2, phosphorene (blackphosphorous), silicene, borophene, tungsten disulfide (WS2), boronnitride, WSe2, stanene (2D tin), graphene, germanane, nickel HITP,Mxenes (Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2, Ti3CN, Nb4C3, Ta4C3),and/or transition metal dichalcogenides. The transistor material may bea bulk transistor material such as Si, amorphous Si, Ge, and/or metaloxide. In particular instances, the channel transistor material may beconfigured so as to extend between a surface portion of the sourceelectrode and a surface portion of the drain electrode. In such aninstance, positioning of the transistor channel nanomaterial between thesource and drain electrodes is designed to form the channel and therebycontrol and/or regulate conductivity between the electrodes. Hence, theFET may include a gate structure.

In certain instances, as herein disclosed, the ChemFET may be configuredfor performing a chemical reaction, such as for the detection of one ormore analytes, such as a reactant from a chemical reaction. Accordingly,in various instances, the FET may include an analyte orreaction-sensitive layer. In various examples, e.g., to facilitate theperformance of a chemical reaction, the ChemFET may include a wellstructure, within which a chemical reaction may take place. Forinstance, one or more of the layers of the FET, such as the first and/orsecond insulating layers may include a chamber, such as a chamber towhich the reactants may be added for the performance of the chemicalreaction. In such an instance, the channel of the ChemFET may be formedwithin the chamber and over the channel so as to electrically connectthe source and the drain electrodes. Further, one or more solutions,such as containing one or more reactants may be added to the chamberthereby forming a solution gate. In various instances, the gatestructure may include the graphene layer.

Further, in various examples, the ChemFET and/or the chamber thereof maybe configured such that the electrodes, e.g., the source and drainelectrodes, are positioned on or in the bounding member of the chamber.For instance, in various instances, the surfaces or walls of the chambermay include one or more trenches, wherein the trench includes one ormore of the electrode structures, and/or may include the 1D or 2Dnanomaterial, such as the graphene layer. Hence, the electrodes of thesource and drain may be included in a bottom or side or circumferentialsurface of the well or trench. In such an instance, an analyte orreaction-sensitive layer may be formed on the well or trench bottomand/or sidewalls and/or may cover the electrodes and/or channelnanomaterial. In some instances, the 1D channel nanomaterial may be avertically-oriented 1D channel nanomaterial. Consequently, the chambermay be configured for sensing and/or measuring the analyte such as areactant that results from the reaction taking place within the chamber.

For example, one or more surfaces of the substrate and/or a well and/ora chamber thereof may be fabricated in such a manner so as incorporatethe electrodes therein. Particularly, one or more of the electrodesdisclosed herein may be formed by any suitable method, such as by beinglithographically photopatterned, which may utilize a light source and/oroptics that allow patterning of deep trenches and/or wells. Moreparticularly, in various instances, an electron beam, laser or plasmabeam may be utilized to pattern the wells and/or trenches and/or theelectrodes. In various instances, the well structure is included ofalternating vertical layers of source and drain electrodes, such as todefine the channel width and the channel length. In particular examples,the well structure is included of electrodes on a well bottom and/or inconjunction with alternating vertical layers of source and drainelectrodes so as to define a channel width and/or channel length.

As stated above, the electrodes may have a transistor channelnanomaterial and/or an analyte or reaction-sensitive material overand/or between them, such as in the alternating vertical layerconfiguration. In various examples, the analyte or reaction-sensitivematerial may be formed by PVD deposition of a metal and oxidization ofthat metal and/or the analyte or reaction-sensitive material may beformed by ALD deposition of a metal oxide, such where the PVD depositionis a sputter or e-beam deposition, and/or the oxidation is a thermal orplasma oxidation. In particular instances, the analyte orreaction-sensitive material may be included of multiple layers, whichmaterial may be formed by any process or a combination of processes soas to cover a bottom and/or side of the well, and in certain instances,the analyte or reaction-sensitive material at the bottom of the well maybe different from the analyte or reaction-sensitive layer coating thewell or trench walls.

Accordingly, in a further aspect of the disclosure, a method forproducing a ChemFET is provided, such as a ChemFET that is configuredfor performing a chemical reaction and sensing one or more of theproducts thereof. In such instances, the ChemFET may include a pluralityof electrodes, and in various instances may be in an alternating,vertical and/or interdigitated layered configuration. In such aninstance, the method may include forming alternating layers of sourceelectrodes, dielectric material and drain electrodes, as well as forminga well or trench within a central portion of the source and drainelectrode patterns. The method may include forming a well or trench inone or more of the layers of the ChemFET, such as one or more of theinsulating layers, such as in an etching process, such as by wet etchingor plasma etching, or the like.

Hence, in various instances, the method for producing a sensor mayinclude forming alternating and/or interdigitated layers of sourceelectrodes, dielectric material, and/or drain electrodes, forming a wellor trench within a central portion of the source and drain electrodepatterns, and/or forming a transistor channel nanomaterial over orbetween the source and drain electrodes, such as where an analyte orreaction-sensitive layer may be formed over the transistor channellayer. For instance, a first layer of transistor channel nanomaterialmay be formed over a first electrode layer, a dielectric layer may beformed over the first electrode layer, a trench may be patterned in thedielectric layer, a second electrode layer may then be formed within thetrench. In various examples, the second electrode layer and dielectriclayer may be planarized, a second layer of transistor channelnanomaterial may then be formed over the second electrode and seconddielectric layer and this process may then be repeated so as to producethe desired number of electrode and channel layers.

Channel Enhancements—Ion Permeable Layer, Ion Getter and Charge TrapScreening Layer

In a further aspect, as seen with respect to FIG. 8, a ChemFET sensor(1) is provided wherein the sensor includes a stacked configurationhaving a plurality of layers and/or structures therein. For instance, aprimary structure (10) includes a semiconductor base layer, e.g., asilicon layer, which is fabricated to contain or may otherwise beconfigured as CMOS circuits. Accordingly, stacked on top of the baselayer (10) may be a secondary structure (20) that may be configured as adielectric layer and/or another inorganic or organic dielectric layer,such as a silicon dioxide layer. The primary (10) and/or secondary (20)structures may additionally include or otherwise be configured tocontain a conductive source (22) and drain (24) embedded in one or moreof the structured layers, and between which is formed a channelstructure (30).

In particular examples, an additional structure or passivation layer(35) may be positioned above the primary and secondary layers, whichpassivation layer (35) may be etched to form one or more well structures(38), which well structure may be coincident with and/or proximate tothe channel sensing region (26) which in turn communicates with asolution gate. In various examples, the nanomaterial channel (30) regionmay include or otherwise be formed by the channel (30) as well as thebounding wall members 39 a and 39 b forming the well structure (38),such as by extending laterally upwards from the surface (21) and/orsensing layer region (26), and having opening (37) positioned therein soas to provide access for the fluid to communicate with the gateelectrode.

The well structure (38) may further include one or more additionalstructures and/or layers, such as a 1D or 2D nanomaterial (30) and/or anoxide (34) and/or passivation (35) layers that may be positioned betweenthe conductive source (22) and drain (24) and/or between wall members(39 a, 39 b) in such a manner as to form a bottom surface and/or sensingzone (26) of the chamber (37). In various instances, one or more of thestructures may further include or otherwise be associated with anintegrated circuit and/or a processor, such as for generating and/orprocessing generated data, such as sensor derived data, e.g., indicativeof a sequencing and/or hybridization reaction taking place within thewell structure (38).

In particular examples, a further structured layer (40), e.g., asecondary or tertiary or quartier structure, may also be provided, suchas where the further structured layer may be included and/or present ona surface (24) or otherwise within the well or chamber (37), such as toenhance the ability of the sensor and/or the processor to determine thedifference between a current and/or voltage applied across the source(22) and/or drain (24) of the transistor, as well as their respectiveassociated charge curves, as described herein.

For instance, in the exemplary example of FIG. 4A, a ChemFET (1) havinga graphene layered channel (30), well structure (38) containing afurther structured layer (40) configured for enhancing the sensitivityof an associated sensor. In this example, the structured well layer (40)is configured as a permeable membrane that may be associated with thegraphene channel (30) and/or analyte or reaction-sensitive (34) layers.Particularly, the ChemFET sensor (1) includes a surface (21), whichsurface may be within a well chamber (37), and be configured as asensing region (26). The surface (21) of the sensing region (26) may becoupled to or otherwise include a 1D or 2D nanomaterial such as agraphene layer configured as a channel (30) for detecting the presenceof one or more chemical and/or biological events and/or elementsresulting thereby.

Accordingly, the surface (21) may be configured as a sensing region(26), and the well chamber (37) may be adapted such that a chemicaland/or biological reaction may take place therein. The surface (26)and/or graphene structured layer (30) may be coupled with or otherwiseinclude an additional structure, such as an ion permeable membrane (40)or an ion getter material (41) or a charge trap layer screening material(42), all of which are configured to enhance the ability of thegraphene-based sensor (1) to detect the presence of a chemical and/orbiological reaction. Particularly, the additional structure (40) may bean ion-selective permeable membrane that is positioned proximate toand/or over a sensing zone (26), which may be configured as a channel(30), and which membrane (40) may be adapted such that it only allowsions of interest to travel through the membrane (40), while excludingthose ions that might cause interference with the sensing capabilitiesof the sensor (1).

Accordingly, as can be seen with respect to FIG. 4A, in variousexamples, the channel sensing region (26) may be configured so as toform a chamber (37) and/or well (38) and the 1D or 2D nanomaterialchannel (30) and/or oxide layer (34) may be positioned between theconductive source (22) and drain (24) in such a manner as to form abottom surface of the chamber (37). In various instances, the structuresmay further include or otherwise be associated with an integratedcircuit and/or a processor, such as for generating and/or processinggenerated data, such as sensor derived data. In various examples asdepicted, such as in FIGS. 4A-4C and other figures illustratedthroughout the disclosure, the ChemFET nanomaterial transistor connectsto a respective drain or source of a semiconductor access transistor(11) positioned at least partially in a substrate layer (10), e.g., asilicon semiconductor. A gate (13) allows control of the semiconductoraccess transistor (11).

Further, in various examples, the chamber (37) may further include amembrane (40) or other element positioned above or between one or moreof the 1D or 2D nanomaterials, or 3D structure layer and/or the oxide(34) and passivation layers (35), such as where the membrane structure(40) is configured for enhancing the ability of the processor todetermine the difference between various I-V and/or I_(d)-V_(gs) curves.For instance, FIG. 7C depicts a graph of an average sensitivity of agraphene FET (“gFET”) calculated as a function of liquid gate potential.The gFET of the present disclosure approaches the theoretical 59 mVoltper pH maximum for an ISFET type device. This sensitivity of the ChemFETis even more enhanced when an ion permeable membrane (40) is included aspart of the device.

In some example, such as seen with respect to FIGS. 4 and 8, a furtherstructured layer (40), e.g., a secondary or tertiary structure, may alsobe provided, such as where the further structured layer may be includedand/or present within the well or chamber, such as to enhance theability of the processor to determine the difference between the currentand/or voltages as well as their respective associated curves. Moreparticularly, the additional structure may include an ion-selectivepermeable membrane (40), such as an ion-selective permeable membranethat allows ions of interest (68) to pass through the membrane (40)while blocking other indeterminate ions, such as to enhance the abilityof the processor to determine the difference between the reference I-Vor I_(d)-V_(gs) curve and the chemical sensing I-V or I_(d)-V_(gs)curve, and thus enhance the ability of the processor to detect a desiredchemical reaction.

In various instances, the ChemFET (1) may be configured such that theI-V or I_(d)-V_(gs) curve(s) may be shifted so as to better respond to,detect, and/or otherwise determine a biological compound or analyteand/or a chemical reaction and or a biologic activity, such as abiological compound and/or a chemical reaction occurring on or near the1D or 2D nanomaterial channel, e.g., graphene, surface (30) of theChemFET (1). In particular instances, the ion-selective permeablemembrane (40) may include a 2D nanomaterial material, e.g., graphene,which may or may not be electrically connected to the source and/ordrain layer and/or channel (30).

Accordingly, in various instances, the ChemFET (1) may be fabricated onan integrated circuit semiconductor wafer that includes a primary (10)and/or secondary (20) structure as well as a channel structure (30), aprocessor and/or a tertiary structure (35), such as a passivationstructure forming one or more wells (38). For instance, the first and/orsecondary structures may include a conductive source (22) and aconductive drain (24), which together with the other components of theChemFET (1) form a channel sensing region (26). The channel (30) extendsfrom the conductive source (22) to the conductive drain 24, with thechannel (30) formed between the two, where a one-dimensional ortwo-dimensional transistor nanomaterial layer (30) may be positionedabove and/or may otherwise be in contact with the source (22) and drain(24).

As indicated above, the ChemFET (1) may include a processor, such aswhere the processor is configured for generating one or more of areference I_(d)-V_(gs) curve and a chemical sensing I_(d)-V_(gs) curve,such as in response to a chemical reaction that is to be detected, forinstance, a reaction occurring over or near a sensing zone (26) of theChemFET (1). In particular examples, the processor is configured fordetermining a difference between the reference I_(d)-V_(gs) curve andthe chemical sensing I_(d)-V_(gs) curve. Hence, in various examples, anadditional structure (40) may be included, such as a structure that isconfigured for enhancing the ability of the processor to determine thisand other associated differences.

Particularly, in various examples, the additional structure may be anion-selective permeable membrane (40) that allows one or more ions ofinterest (68) to pass through the membrane (40) while blocking otherions. More particularly, the additional structure (40) may be configuredso as to enhance the ability of the processor to determine thedifference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve (or corresponding parameters thereof), andthus further enhances the ability of the processor to detect a desiredchemical reaction. Accordingly, in various instances, the ion-selectivepermeable membrane (40) may be positioned within the well (38) and/orover a passivation layer (35), an ion sensitive or sensing layer (34), a1D and/or a 2D transistor material layer (30), and/or a dielectric layer(35) that itself may be positioned over and/or otherwise form a part ofthe chamber (37) or channel sensing region (26).

In particular instances, the ion-selective permeable structure (40) mayinclude a polymer such as perfluorosulphonic material, aperfluorocarboxylic material, PEEK, PBI, Nafion or PTFE. In otherinstances, the ion-selective permeable structure may be composed of aninorganic material such as an oxide or a glass. In particular instances,the ion-selective permeable structure (40) may be applied to a surface(e.g., 21) of the ChemFET (1) such as by being deposited thereon, suchas by a spincoating, anodization, PVD, CVD, sol gel or other methods. Anadditional material, e.g., HMDS, may also be included so as to managethe interaction of the chamber (37) and/or channel (30) and/orassociated dielectric layer (20) and/or an underlying 2D or 1Dnanomaterial transistor layer (30).

For instance, a ChemFET (1) of the disclosure may include an additionalstructure that includes a 2D nanomaterial transistor channel or surfacethat may include an ion-sensitive material (34) over the channel orsurface. In such an instance, the material may be sensitive to ions thatare different from the ions associated with the biological molecule orchemical reaction that is to be detected. Particularly, theion-selective permeable structure (40) may additionally be composed ofan ion sensitive 1D or 2D transistor nanomaterial, such as graphene,that is in addition to the 1D or 2D nanomaterial layer 30, and is notelectrically connected to the channel (30).

In certain examples, as depicted in FIG. 4B, the ChemFET may include anion getter material (41), such as an ion getter material (41) that trapsor sequesters ions (69) that are not relevant to the biological speciesand/or chemical reaction to be sensed and/or determined, such as toenhance the ability of the processor to determine the difference betweenthe reference I-V or I_(d)-V_(gs) curve and/or the chemical sensing I-Vor I_(d)-V_(gs) curve. This may be useful because reducing the numberand/or the amount of interfering ions (69), enhances the ability of theprocessor to detect the desired biological species and/or results of thechemical reactions.

Particularly, the ion getter material (41) may be arranged withinproximity to the chamber (37) and/or surface (21) thereof so that theaction of gettering the unwanted ions improves the detection capabilityof the ChemFET (1). In some instances, one or more of the various layersherein, such as the ion getter material (41) may be placed over orbetween one or more of the other layers, such as the dielectric layer(20/35), oxide layer (34), or 2D or 1D nanomaterial layers (30),positioned in proximity to one or more of the chambers, channels, orsurfaces of the ChemFET device (1). In yet another alternative thegetter material (41) a may be positioned within the chamber (37), suchas on a wall (39 a and/or 39 b) thereof, and/or in a package that isadapted to attract unwanted ions.

In certain instances, the ion getter structure (41) may be positionedover or near the ion sensitive layer (34) that itself may be positionedover the channel structure or surface (30) or may be position over ornear the well structure (38) such as on a top surface of the well or ona sidewall (39) of the well. The ion getter material (41) is configuredto trap ions that are not relevant (69) to the chemical reaction to bedetermined, such as trapping Na+ ions if H+ ions are the ions ofinterest. Accordingly, in some instances, a suitably configured iongetter material (41) may be useful because the action of sensing ionsthat are different from the ions associated with the biologics and/orchemical reactions that are to be detected allows the processor tofilter out the signal from the unwanted ions from the signal of the ionsof interest.

The ion getter material (41) may be a metal such as a barium orzirconium alloy, or preferably is a glass such as phosphorous-silicateglass (PSG), argon-silicate glass or arsenic-silicate glass. Thesegetter materials may be especially adept at trapping sodium ions, whichmay be present due to the buffers used in the fluid. A preferred iongetter material (41) is a 4 to 8% by weight phosphorous-silicate glass(PSG) that is deposited by a CVD process to a thickness of about 10 to30 nm

In particular instances as shown in FIG. 4C, an insulating material (42)may be placed over the dielectric layer (20) and under the 1D or 2Dnanomaterial channel layer (30) in order to screen the sensing region(26) from the dielectric layer (20). The dielectric layer (20),typically a silicon oxide, may charge traps within the layer or at theinterface between the layer (20) and the channel (30). Furthermore, thedielectric layer (20), especially if a silicon oxide, is not atomicallysmooth and thus affects the carrier mobility through the channel (30).An appropriate screening material (42) can serve to screen the trappedcharges from the channel sensing region (26) and if it also has a smoothsurface, it can enhance carrier mobility through the channel (30). Apolymer such as an HMDS material or other siloxane or parylene may bepositioned under the graphene channel (30) to act as the charge trapscreening layer (42). Alternatively, an inorganic material, such asaluminum oxide or preferably hexagonal boron nitride (hBN) may be usedas the charge trap screening layer (42).

Accordingly, in various instances, an exemplary ion-selective permeablemembrane (40) and/or an additional getter structure (41) may bepositioned over or near a channel sensing region (26), where thesestructures are configured so as to only allow ions of interest (68) totravel to the sensing region (26). In particular instances, the gettermaterial may be positioned within the chamber (37) or elsewhere on thechip or in the package so as to trap or sequester unwanted ions. Anotheralternative would be to include another ion-selective functionallayer(s) over some of the sensors that can detect the presence ofunwanted ions (69) so that their interaction with the sensor and thusthe determination of the sensor reaction to the desired ion can befiltered out.

In all of these instances, the action of trapping ions that are notrelevant to the chemical reaction to be determined enhances the abilityof the processor to determine the difference between the reference I-Vgcurve and the chemical sensing I-Vg curve, e.g., because there are fewerinterfering ions. In such instances, the membrane (40) and/or ion gettermaterial (41) may be arranged within proximity to a sensing zone (26)that is in proximity to a channel (30) so that the action of getteringthe unwanted ions improves the detection capability of the ChemFET.Alternatively, the ion getter material (41) may be placed over adielectric layer that is in proximity to one or more of the sensingzones (26) and/or channels.

In yet another example, a charge trap screening material (42) may bedeposited or formed under the channel layer (30), i.e., beforedepositing or forming the channel (30), such charge trap screening layer(42) effectively screening the channel sensing region (26) from chargestrapped in the dielectric layer (20). Furthermore, the charge trapscreening layer (42) may be smoother than the dielectric layer (20) forimproving the mobility of the charge carriers traveling through thechannel (30). The charge trap screening layer (42) may be formed of HMDSor another siloxane, parylene, hexagonal boron nitride (hBN), aluminumoxide or other material, hBN is a preferred material due to its atomicsmoothness, close lattice match to graphene (their lattice parametersvary by less than 2%) and lack of dangling bonds that otherwise mighttrap charges.

ChemFET Reference Electrode

Additionally, as indicated, in certain instances, the ChemFET mayinclude a reference electrode that may be composed of Ru, Pd, Ag, Os,Ir, Pt, Au, Rh, or Ag/AgCl. In certain instances, the referenceelectrode may be positioned so as to be in electrical communication withthe ChemFET, such as through a fluid or solution. In such an instance,the reference electrode may be used to apply a gate voltage to theChemFET, optionally through the fluid or solution. Hence, the referenceelectrode may include at least a portion of a metal layer, such as overor on an integrated circuit structure.

Particularly, the reference electrode may be incorporated in a layer ofthe integrated circuit chip structure that includes the ChemFET, such asa topmost layer of the integrated circuit structure, or a layer adjacentto one or more ChemFETs on the integrated circuit structure. However, invarious instances, the metal layer optionally is part of a separatepiece that is attached or affixed to the integrated circuit chip,optionally using a glue, adhesive, polymer, or thermoplastic, or thelike. Regardless, the reference electrode is configured so as to be inelectrical communication with an interconnect on the integrated circuitstructure, such as where the interconnect optionally is (i) integrallyconnected to the reference electrode through a common metal layer on theintegrated circuit, or (ii) connected to the reference electrode througha wirebond, flip-chip, or conductive adhesive connection structure,which connection may optionally be sealed from the fluid or solutionwhile another portion of the reference electrode may be in communicationwith the fluid or solution.

In certain instances, the reference electrode may be incorporated withina package and/or housing of the integrated circuit structure. Forinstance, the reference electrode may include at least a portion of ametal layer, e.g., over or on the package substrate or package lid,wherein the metal layer optionally is part of a separate piece that isattached or affixed to the package substrate or package lid, such asusing a glue, adhesive, polymer, or thermoplastic, and/or the like.Hence, in particular instances, the reference electrode may be a metallayer deposited by a method that is a PVD, CVD, printing,electroplating, an electroless plating method, and/or the like. In someexamples, the reference electrode may include two or more referenceelectrode elements.

As described, an array according to the disclosure that includes aplurality of sensors may also further include one or more referenceelectrodes (66), preferably platinum or Ag/AgCl reference electrodes(66), which are used to apply a gate voltage to the fluid and thus toeach of the ChemFETs in the array of ChemFETs on the ChemFET sensor ICchip.

As shown in the following figures, reference electrodes (66) can also beutilized with the ChemFET-based sensors and devices of the disclosure.There are multiple reference electrode (66) options for use withchemically sensitive sensors. For example, platinum, silver, or otherfluid-compatible reference electrodes (66), such as noble metal Ru, Pd,Ag, Os, Ir, Pt, Au, Rh, or Ag/AgCl, can be used. For example, thematerial for the reference electrodes (66) can be deposited on (orotherwise applied to) the chip surface (e.g., by PVD or CVD). Thereference electrodes (66) can then be directly coupled to the conductivelines, e.g., copper lines, forming the other electrodes. Anotherapproach is to plate the reference electrodes (66) on the chip (using anelectroless plating process). Yet another approach is to have thereference electrodes (66) as separate pieces adhesively attached to thechip (preferably including overactive peripheral circuitry so as toconserve space and not interfere with the wells or other sensing regionsof the device) and wirebond interconnected or attached to the package orthe chip. Yet another example includes reference electrodes (66) asseveral pieces as in FIG. 15 so that resistance through the fluid to thereference electrode is more normalized.

Other examples have the reference electrodes (66) incorporated as ametallization layer deposited on top of the wells (e.g., by sputtering,evaporation, or plating). The reference electrode(s) (66) is(are)connected separately from the chip interconnect using wirebonds (46) tothe package substrate bond pads (49) as depicted in FIG. 12.

Thus, in some examples the chemically-sensitive sensor is based on aChemFET sensor IC chip (50) according to the disclosure fabricated on anintegrated circuit wafer, which ChemFET sensor IC chip (50) alsoincludes a processor and one or more reference electrodes (66). Theprocessor is configured to determine a chemical reaction based on theelectrical characteristics of the ChemFET (1). The reference electrode(66) is preferably selected from the group of Ru, Pd, Ag, Os, Ir, Pt,Au, Rh, and Ag/AgCl

The reference electrode (66) is preferably in electrical communicationwith a ChemFET (1), and is preferably used to apply a gate voltage tothe ChemFET (1). The reference electrode can alternatively be used toapply a gate voltage to the ChemFET (1) through a fluid or solution.

The reference electrode (66) is preferably included of at least aportion of a metal layer over or on the integrated circuit chip.

In one example, the reference electrode (66) is incorporated in a layerof a ChemFET sensor IC chip (50) that includes the ChemFET (1). In otherexamples, the metal layer is part of a separate piece that is attachedor affixed to the integrated circuit chip.

In some examples, the reference electrode(s) (66) is (are) attached oraffixed to the integrated circuit chip by a material comprising a glue,adhesive, polymer, or thermoplastic.

In some preferred examples, the reference electrode (66) is inelectrical communication with an interconnect on the integrated circuitchip. The interconnect is integrally connected to the referenceelectrode through a common metal layer on the integrated circuit chip,or the interconnect is connected to the reference electrode (66) througha wirebond, flip chip, or conductive adhesive connection. In certainexamples, the wirebond, flip chip, or conductive adhesive connection toa portion of the reference electrode (66) is sealed from the fluid orsolution while another portion of the reference electrode (66) is incommunication with the fluid or solution.

In some examples, a reference electrode layer (66) is a topmost layer ofthe integrated circuit. In some examples, a reference electrode layer(66) is adjacent to one or more ChemFETs (1) on the ChemFET sensor ICchip (50). In other examples, the reference electrode (66) isincorporated within the package housing the ChemFET sensor IC chip (50).In certain examples, the reference electrode (66) includes at least aportion of a metal layer over or on the package substrate or packagelid, while in other examples, the metal layer is part of a separatepiece that is attached or affixed to the package substrate or packagelid. In certain examples, the reference electrode (66) is attached oraffixed to the package substrate or package lid by a material comprisinga glue, adhesive, polymer, or thermoplastic. In various examples, areference electrode (66) is in electrical communication with aninterconnect on the package substrate or package lid.

In some examples, the interconnect is integrally connected to thereference electrode (66) through a common metal layer on the packagesubstrate or package lid. In some examples, the interconnect isconnected to the reference electrode (66) through a wirebond, flip chip,solder, or conductive adhesive connection. In certain examples, thewirebond, flip chip, solder, or conductive adhesive connection to aportion of the reference electrode (66) is sealed from the fluid orsolution while another portion of the reference electrode (66) is incommunication with the fluid or solution. In various examples, thereference electrode (66) layer is a topmost layer of the packagesubstrate or a bottommost layer of the package lid. In another example,the reference electrode (66) layer is adjacent to one or more ChemFETs(1) on the ChemFET sensor IC chip (50). The metal layer is deposited bya method included of a PVD, CVD, printing, electroplating, orelectroless plating method. In some preferred examples, the devicesinclude multiple reference electrodes (66).

Accordingly, in one aspect, a ChemFET sensor IC chip (50) may beprovided. The ChemFET sensor IC chip (50) may include an integratedcircuit structure, such as a CMOS structure, and may also include aconductive source (22) and a conductive drain (24), which source anddrain may be separated one from the other so as to form a channel (30)region. Hence, in various examples, a nanomaterial channel (30) may beincluded where the channel (30) extends at least from the conductivesource (22) to the conductive drain (24). In particular implementations,the channel (30) may be composed of a channel nanomaterial such as aone-dimensional transistor nanomaterial or a two-dimensional transistornanomaterial, such as where the conductance of the channel shifts inresponse to a chemical reaction occurring over or near, e.g., proximate,the channel (30).

In various instances, the length of the channel from an inside oroutside edge of the source to the drain may range from 0.05 micron to 3microns, and may have a width of the conductive channel that ranges from0.05 micron to 2 microns for a rectangular channel (30). However, inother examples where the objective is to increase the channel W/L ratio,the effective channel width may be very large, such as 10 microns, or100 microns or more.

Particularly, in certain examples, the channel may include aone-dimensional, e.g., carbon nanotube or semiconductor nanowiretransistor material, or a two-dimensional transistor material, such asone or more of graphene, silicene, molybdenum disulfide, blackphosphorous (phosphorene), borophene, tungsten disulfide, boron nitride,tungsten diselenide, stanene, germanane, nickel HITP, and/or metaldichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2,Ti3CN, Nb4C3, or Ta4C3. Additionally, in some examples, anon-conductive, e.g., an oxide, layer may be disposed over the channel(30) nanomaterial, which layer may be a thin layer, such as having athickness of 50 nanometers or less.

ChemFET Gate Structure

FIG. 7A depicts a ChemFET configured with a solution gate. In thisinstance a nanomaterial channel (30) connects a conductive source (22)and drain (24) and a fluid (64) contained within a chamber (37) of awell structure (38) has a gate voltage applied to it by a gate orreference electrode (66). The gate voltage level affects the conductancethrough the channel (30). This configuration is referred to as asolution gated ChemFET. The solution gate can be considered a top gatesince the fluid is on top or over of the channel.

The ChemFET of FIG. 7A may have a maximum sensitivity due to the natureof its operation and also the material chosen for the ion sensitivelayer (34). FIG. 7C shows a graph of sensitivity versus solution gatevoltage for a ChemFET represented in FIG. 7A. There is an upper boundfor sensitivity, referred to as the Nernst limit, of 59 mV/pH.

In another example the ChemFET transistor can be fashioned with a bottomor back gate, i.e., a gate oriented underneath the channel. One way tocreate a backgate is to bias the whole semiconductor substrate 10 with adesired gate voltage. In this case all the ChemFETs (1) on a ChemFETsensor IC chip (50) as shown in FIG. 15B will have the same appliedbackgate voltage. This scheme is referred to as a global backgate.

In a further example of the ChemFET transistor an individual backgate(82) for each ChemFET may be provided as shown in FIG. 7B. Since thereis a backgate for each ChemFET this is called a local backgateconfiguration. In this case the backgate (82) is included of aninterconnect material. The advantage of a local backgate is that itsvoltage may be tuned or optimized for the particular characteristics ofthe ChemFET to which it is associated.

It is possible to operate a ChemFET (1) with more than just a singlegate, i.e., the ChemFET, such as shown in FIG. 7B, may have both asolution gate (top gate) and a backgate (local backgate (82) or globalbackgate (not shown)) in operation at the same time. This is referred toas a dual gate and has the benefit of more gate control over the channel(30) or when used as a sensor for providing improved ChemFETsensitivity—even to the point of achieving sensitivity higher than theNernst limit of 59 mV/pH.

Extending this concept further is a Gate All Around (GAA) configurationwhere a portion of the channel (30) is fully surrounded by gatematerial. This may be the best gate configuration for a ChemFET toachieve its maximum sensitivity. FIG. 9C depicts a ChemFET (1) with agate all around (GAA) configuration. In this case the gate material isthe fluid 64 to which is applied a gate voltage through the gate orreference electrode (66). It will be noted that the fluid completelysurrounds the central portion of the channel (30).

In one instance the gate all around structure is achieved by providingan etch stop structure (74) configured as a tub-like shape andpositioned in the dielectric material (20) under the channel (30) asshown in FIG. 9A. FIG. 9B depicts the ChemFET (1) after the wellstructure (38) has been formed and after the dielectric (20) under thechannel and within the etch stop layer-defined tub has been etched away.In this example the etch is preferably a wet chemical etch and not adry, e.g., plasma, etch since dry etch processes tend to damage ordestroy the graphene. A suitable wet etchant is a hydrofluoric (HF)acid-based etchant, such as a mixture of HF and a buffer such asammonium fluoride. This etchant has high selectivity to silicon dioxidein comparison to silicon and thus silicon of the sensor IC chip wafershould not be damaged. Furthermore, an HF-based etch should not have badeffect on the graphene channel (30).

In a second instance of the preferred gate all around structure, thegraphene is first deposited or formed on a metal interconnect material(25) that may form one of the source (22) or drain (24) conductiveelectrodes as shown in FIG. 10A. If the interconnect material is copper,such as formed in trenches in a damascene process and with the upperportions of the electrodes exposed to the surface, i.e., copper isexposed to the surface then the possibility exists for forming thegraphene (i.e., growing the graphene) directly on the semiconductor ICwafer rather than on a separate growth wafer and then transferring thegraphene to the IC wafer. This may be possible since copper is one ofthe preferred growth substrates for graphene (graphene does not diffuseinto copper during the growth) and if the growth temperature is kept lowenough, such as lower than 400 C, so as not to affect the semiconductortransistors, such as CMOS transistors.

It may be possible that a plasma-enhanced CVD (PECVD) or other enhancedCVD process will allow growth of good quality graphene directly on theexposed copper surfaces on an IC wafer. Once the graphene is formed ordeposited on the copper areas, such as shown in FIG. 10A then in asubsequent process step the dielectric underlying the channel area (26),which at this time includes both graphene and a thin layer of copper, isetched. For a silicon dioxide dielectric, a wet HF acid etchant issuitable. The etch may be further controlled or confined by an etch stoplayer (74) formed in a tub-like shape. As depicted in FIG. 10B. Finally,the thin copper layer under the graphene channel (30) can be etched by asuitable copper etchant, such as ammonium persulfate or ferric chloride,resulting in the central portion of the graphene channel to be free ofany dielectric, as shown in FIG. 10C, and available for contact by thefluid to form a gate all around structure as shown in FIG. 9C.

In another gate all around example, as shown in FIG. 11A, there is noetch stop layer provided under the channel sensing region (26). In thiscase the wet etching of the silicon dioxide dielectric (20) will beisotropic and will result in a bowl-shaped cavity beneath the channel(30) as shown in FIG. 11B. Furthermore, since the etching is notconfined by an etch stop layer, the etched cavity may not be fullyuniform in size and shape.

ChemFET Electrical Operation and Sensing

As indicated above, in particular examples, the FET can be adapted so asto be cavitated so as to include one or more sensing chambers that arepositioned so as to align with a channel region of the FET. In suchinstances, the FET may be in contact with a fluidic source so as to forman ISFET or more specifically a solution-gated ChemFET. Accordingly, theChemFET may be configured to run one or more chemical and/or biologicalreactions within its various chambers, such as a DNA hybridization orsequencing reaction, and the like or to detect an analyte or detectbiologic activity, such as proximate a solution gated sensing zone.

For these purposes, the ChemFET may include or be coupled with aprocessor configured for detecting the one or more reactions, analytes,or biologic activity, e.g., involving a biological or chemical material,so as to obtain reaction, analyte, or biologic activity results, and foranalyzing those results, for instance, based on detecting and/ormeasuring changes in a voltage (V) potential, current (I), charge (Q) orcapacitance (C) occurring within the channel region on the ChemFET.

Particularly, as can be seen with respect to FIG. 15E, the processor,such as a signal processor 151, may be configured so as to generate oneor more current (I) vs. voltage (V) curves, such as where the current Idof the I_(d)-V_(gs) curve is the current flowing through the drain (24)of the chemically-sensitive solution gated ChemFET and/or where the gatevoltage (Vgs) of the I_(d)-V_(gs) curve is the voltage potential appliedbetween the gate and the source of the ChemFET (1). In such an instance,the gate voltage Vgs of the I_(d)-V_(gs) curve may be a top and/or aback gate voltage that may be applied to the ChemFET (1) through a top(or front) and/or back of the device, respectively.

In particular examples, the gate voltage Vgs of the I_(d)-V_(gs) curvemay be a solution gate voltage such as applied to the chemicallysensitive FET through a solution flowed over a portion, e.g., a chamber(38), of the device (1). In some examples, the reference I_(d)-V_(gs)curve and/or a chemical sensing I_(d)-V_(gs) curve (or a correspondingparameter, e.g., a slope, of such reference and sensing curves) may begenerated in response to the analyte, biologic activity and/or chemicalreaction that is to be detected and/or occurs over or near the ChemFET,such as within a chamber or well (38) of the ChemFET structure. Invarious examples, the processor (150) may be configured to determinedifferences in relationships between a generated reference I_(d)-V_(gs)curve and/or chemical sensing I_(d)-V_(gs) curve.

In certain instances, a circuitry component (140) may be included wherethe circuitry component may include at least one analog-to-digitalconverter (141) that is configured for converting analog signals, suchas obtained as a result of the performance of the reaction(s) within thesensing well (38), or array of wells, into digital signals, such as maybe sent back to the processor or computing component (150) for furtherprocessing.

Accordingly, in another aspect of the disclosure, a ChemFET(1) may beprovided, wherein the device may include a structure having a conductivesource (22) and drain (24) as well as having a surface or channel (30)extending from the conductive source to the conductive drain, such aswhere the surface or channel includes a 1D or 2D transistor nanomaterial(30). The device (1) may also include a computing component (150) havingor otherwise being associated with a processor (140) such as where theprocessor (140) is configured for generating a reference I_(d)-V_(gs)curve and/or generating a chemical sensing I_(d)-V_(gs) curve, inresponse to the chemical reaction, biologic activity or analyteoccurring within a chamber (37) of the ChemFET (1), and may beconfigured to determine a difference between the reference I_(d)-V_(gs)curve and the chemical sensing I_(d)-V_(gs) curve.

Specifically, FIG. 13A depicts a graph illustrating an I_(d)-V_(gs)curve calling out some of the various characteristics that may be usedto categorize I_(d)-V_(gs) curves, and FIG. 13B depicts a graph of anI_(d)-V_(gs) curve illustrating the results of a single difference andthat of multiple differences.

Particularly, as can be seen with respect to FIG. 13B, the differencebetween the reference I_(d)-V_(gs) curve measurement and the chemicalsensing I_(d)-V_(gs) curve (or corresponding parameters thereof)measurement is a shift in a minimum point of the Vgs value of thechemical sensing I_(d)-V_(gs) curve relative to a minimum point of theVgs value of the reference I_(d)-V_(gs) curve. As can be seen, thisshift is from left to right along the Vgs axis. Hence, as can be seenwith respect to FIG. 13C, in some instances, a change in reactionconditions, biologic activity or analyte that result in a change in theI_(d)-V_(gs) curve may be demarcated by a shift in the I_(d)-V_(gs)curve, or as depicted in FIG. 13D, it may be demarcated by a change inthe shape of the I_(d)-V_(gs) curve.

More particularly, as exemplified in FIG. 13C, in one example, thedifference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve may be a change in the slope of the chemicalsensing I_(d)-V_(gs) curve relative to a change in the slope of thereference I_(d)-V_(gs) curve. Likewise, as exemplified in FIG. 13D, thedifference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve may be an overall change in the shape of thechemical sensing Id-Vgs curve relative to an overall change in shape ofthe reference I_(d)-V_(gs) curve.

In other instances, as can be seen with respect to FIGS. 13E and 13F,the difference between the reference I_(d)-V_(gs) curve and the chemicalsensing I_(d)-V_(gs) curve may be a shift in an Ion value of thechemical sensing I_(d)-V_(gs) curve relative to a shift in an Ion valueof the reference I_(d)-V_(gs) curve, for instance, where the Ion valuesare taken from a p-type (FIG. 13E) or n-type (FIG. 13F) section of theI_(d)-V_(gs) curve (see FIG. 13A). For example, the measurements of theslopes may be taken from the steepest and/or flattest sections on thep-type and/or n-type portions of the I_(d)-V_(gs) curves. Specifically,FIGS. 13E and 13F depict graphs of I_(d)-V_(gs) curves illustrating achange in the level of the I_(d)-V_(gs) curve where the Ion is in ap-type region (FIG. 13E), and a change in the level of the I_(d)-V_(gs)curve where the Ion is in a n-type region (FIG. 13F).

Additionally, in particular instances, the difference between thereference Id-Vgs curve and the chemical sensing I_(d)-V_(gs) curve (orcorresponding parameters thereof) may be a shift in an Ioff value of thechemical sensing I_(d)-V_(gs) curve relative to an Ioff value of thereference I_(d)-V_(gs) curve. Particularly, FIG. 13G depicts a graph ofan I_(d)-V_(gs) curve illustrating a change in the level of theI_(d)-V_(gs) curve (Ioff). More particularly, in such examples, asdepicted in FIG. 13H, the difference in the overall shape of theI_(d)-V_(gs) curves may be determined by first fitting a polynomial orother fitting line to each of the v curves and then comparing thecoefficients of those fitting lines. Specifically, FIG. 13H depicts agraph of an I_(d)-V_(gs) curve illustrating a fit polynomial or otherfitting line to curve and use coefficients as read criterion.

In other examples, the difference between a reference I_(d)-V_(gs) curveand the chemical sensing I_(d)-V_(gs) curve is based on more than onechemical sensing I_(d)-V_(gs) curve. Further, FIG. 13I depicts a graphof an I_(d)-V_(gs) curve illustrating a slope of the I_(d)-V_(gs) curveon one or both sides of the curve (it may be noted that the slope ofthis curve is the transconductance gm, which is proportional to carriermobility). The use of a solution gate and backgate in combination (adual gate) can be used to improve signal strength and to changecharacteristics of I-V curve. Likewise, a gate all-around structure willchange the characteristics of the ChemFET characterization curves.

It is to be noted, with respect to FIGS. 18A and 18B, when no microbead(60) is present in the well structure (38), an electric signal may betransmitted to the processor (140) or computing component (150). In suchan instance, the processor may be configured to eliminate from themeasurement the number of wells (38) that are unoccupied, or at least tocompensate in the measurement for the number of wells (38) that areunoccupied, such as where the measurement may be a shift in the I-Vgcurve and/or I_(d)-V_(gs) curve (or corresponding parameters thereof).Likewise, as shown in FIG. 18C, when two or more microbeads (60 a, 60 b)are present in the well structure (38), an electric signal may betransmitted to the processor (140) or computing component (150).

In such an instance, the processor may be configured to eliminate fromthe measurement the number of wells (38) containing multiple microbeads60, or at least compensate in the measurement for the number of wells(38) containing multiple microbeads (60), such as where the measurementmay be recognized as a shift in the I-V curves or reference and sensingI_(d)-V_(gs) curves. In some instances, a calibration of the ChemFETsensor array chip may be done prior to its use for detecting a specificanalyte, biologic activity, or chemical reaction. The calibrationprocedure may determine wells or sensing locations that have nomicrobeads or more than one microbead and this information can be storedfor later use by a processor (140) or computing component (150) tocompensate for wells or sensing locations with no microbeads or multiplemicrobeads.

Accordingly, as can be seen with respect to FIGS. 13A-13I, in particularexamples, the FET and/or processor (140) may be configured to respond toa shift in the I-V or I_(d)-V_(gs) curve, such as where the curve isshifted in response to the detection of a biological compound and/or theresult of a reaction taking place in or on a surface (21) of the FETdevice (1). In some instances, the I-V/I_(d)-V_(gs) curve may beproduced and/or shifted in response to a chemical reaction occurring ona sensing layer (34) and/or the surface of a 1D or 2D nanomaterial,e.g., graphene, channel (30) of the field effect transistor (1), such asresulting from the detection of a biological compound or reactionoccurring within the well structure (38) of the device. Hence, the FETand/or processor may be configured so as to shift the I-V curve orI_(d)-V_(gs) curve such as in response to the chemical reaction.

It should be noted that FIGS. 13A-13I show I-V curves characteristic ofa ChemFET with a graphene nanomaterial channel, i.e., the curves areambipolar (showing both n-type and p-type characteristics within thesame transistor). Other ChemFETs with different 1D or 2D nanomaterialchannels will have different characteristic curves, however; thetechnique of comparing a reference curve to a sensing curve to detect ananalyte, biologic activity, or chemical reaction proximate a ChemFET isstill valid.

For instance, FIG. 14B depicts a graph of an I_(d)-V_(gs) curve forvarious pH values. Particularly, FIG. 14B illustrates the transfercharacteristics of a 20×40 micron graphene-on-SiO2 solution gatedChemFET at a constant drain-source voltage of Vds=50 mV for different pHvalues. FIG. 14C depicts a graph of current increase versus pH increase.Likewise, FIG. 14D depicts a graph of frequency vs. normalized powerspectral density for a silicon ISFET device. FIG. 14E illustrates agraph of frequency vs. normalized power spectral density for a typicalgraphene ChemFET device of the disclosure. Additionally, FIG. 14Fdepicts a graph of frequency vs. normalized power spectral density for agraphene ChemFET of the disclosure. FIG. 14G depicts a graph of noisevs. bias voltage, and FIG. 14H depicts a graph of Dirac voltage vs.current increase.

Sequencing with the ChemFET

Accordingly, when using the device for sequencing a nucleic acid sample,the target nucleic acid sample (62) may be coupled to, immobilized on,or in proximity with the sensing zone (26) of the ChemFET (1). Thistemplate sequence (62) may then be sequenced and/or analyzed byperforming one or more of the following steps. For example, a primer,and/or a polymerase, e.g., an RNA and/or DNA polymerase, and/or one ormore substrates, e.g., deoxynucleotide triphosphates dATP, dGTP, dCTP,and dTTP, may be added, e.g., sequentially, to the sensing chamber (37),to facilitate a polymerase-mediated elongation reaction. Once theappropriate substrate is incorporated into the growing DNA strand, therewill be a concomitant change in the individual electrical characteristicof the associated ChemFET (1), such as a change in voltage, e.g., thesource-drain voltage (V_(sd)), or the drain current I_(d) measured as aresult of the new local gating effect.

Hence, for every elongation reaction with the appropriate, e.g.,complementary, substrate there will be a change in the characteristicvoltage or current or a change in the transfer characteristic of theChemFET (for example in the I_(d)-V_(gs) curve). For instance, asdescribed herein, a ChemFET device (1) for nucleic acid sequencingand/or gene detection is disposed in a sample chamber (37) of a flowcell, and a sample solution (64), e.g., containing a polymerase and oneor more substrates, may be introduced to the sample solution chamber(37). In various examples, a reference electrode (66) may be disposedupstream, downstream, or in fluid contact with the ChemFET device (1)and/or the source and/or drain may themselves serve as electrodes, suchas for hybridization detection, and gate voltage may be applied wheneverneeded.

Particularly, in an exemplary elongation reaction, polynucleotides aresynthesized if the added substrate is complementary to the next unpairedbase of the template nucleic acid. If the added substrate is notcomplementary to the next available base, base-pairing does not occurand there is no elongation. Since nucleic acids, such as DNAs and RNAs,have a negative charge in aqueous solutions, hybridization resulting inelongation can be incrementally determined by the change in the chargedensity in the sensing chamber (37). And because the substrates areadded sequentially, it can readily be determined which nucleotide boundto the template to facilitate the elongation reaction. Accordingly, as aresult of elongation, the negative charge on the graphene channelsurface, sensing layer surface, and/or the sidewall surface of thesensing chamber will be increased. This increase can then be detected,such as a change in the gate source voltage, as described in detailherein. By determining which nucleotide substrate resulted in a signalof change in gate-source voltage, the base sequence identity of thetarget nucleic acid can be determined and/or analyzed.

More specifically, the ChemFET (1), such as for nucleic acid elongationand/or hybridization detection, may be associated with a salt or analytesolution that is added to the sensing chamber (37), which can then beused to determine if an elongation reaction has taken place.Particularly, once the template is associated with the substrate, thereaction mixture containing a polymerase, e.g., a DNA polymerase, and afirst nucleic acid substrate, e.g., dATP, is added to the buffersolution to facilitate an elongation reaction on or in proximity to thegraphene channel (30) or the coated sensing layer (34) of the sensingchamber (37) surface. If the dATP is a complement to the next availablereaction site in the isolated template, a binding event, i.e.,base-pairing, will occur and the antisense strand of the growingsequence will be elongated, which elongation can be detected by the gFETtransistor.

For example, if adenine (A) is complementary to the base thymine (T) onthe target template adjacent to the 3′-terminus of the nucleic acidtemplate, an elongation reaction occurs, resulting in thepolymerase-mediated addition of one adenine base to the growing DNAstrand. In such instance, an enzyme, e.g., DNA polymerase, and thesubstrate may be washed away from the gate portion and sensing chamber,and a buffer solution, e.g., a phosphoric acid buffer solution, e.g.,having a pH of about 6, may be introduced on the graphene gate surfaceto measure changes in the source-drain voltage. If hybridizationoccurred, there will be a change in the source-drain voltage and it willbe detected.

However, if the dATP is not a match, there will be no hybridization, andif no hybridization, there will be no elongation and no correspondingsignal detected by ChemFET (1) of the well (38) in which the reactionmixture was present. Thereafter, another reaction mixture containinganother, different nucleotide substrate, e.g., dCTP, the polymeraseenzyme, and other necessary reagents are added to the sensing chamber(37) under conditions suitable for polymerization if base-pairing occursbetween the next nucleotide in the template and the added dCTP. Ifelongation occurs, it will be detected by the gFET. These steps arerepeated until the nucleic acid sample has been completely sequenced. Invarious instances, the temperature within the sensing chamber may becontrolled, for instance, it may be set to 74° C., such as by using atemperature sensor and/or a heater integrated in the field-effectdevice.

If an elongation reaction takes place there will be a resultant changeto the Dirac voltage (for a gFET), which will be increased, e.g., by 4mV, from before the elongation reaction. The shift of the Dirac voltagein the positive direction indicates that a negative charge was generatedon the graphene channel surface. It can be understood from this thatpolymerization of one base to the growing DNA daughter strand caused bythe elongation reaction was detectable as a change in Dirac voltage. Asecond elongation reaction may then take place and be repeated until theentire target nucleic acid has been sequenced.

ChemFET Sensor Array IC Chip and System

In some examples, as can be seen with respect to FIGS. 15A and 15B, aChemFET sensor IC chip (50) may include a plurality of wells (38),having a plurality of openings (37), where each well (38) is associatedwith one or more sensors, and may thus be configured as an array, e.g.,a sensor array. Such an array or arrays may be employed to detect thepresence and/or a change in concentration of various analyte types, achemical reaction, or a biologic activity, such as within the wells(38), in a wide variety of chemical and/or biological processes,including DNA hybridization and/or sequencing reactions. For instance,the devices herein described and/or systems including the same may beemployed in a method for the analysis of biological or chemicalmaterials, chemical reactions, or biologic activity, such as for wholegenome analysis, genome typing analysis, microarray analysis, panelsanalysis, exome analysis, microbial/microbiome analysis, genotypinganalysis, and/or clinical analysis, such as cancer analysis, NIPTanalysis, cfDNA, blood/plasma/serum analysis, and/or UCS analysis.

In a particular example, as depicted in FIG. 15A or 15B, a multiplicityof the wells (38) of the ChemFET device may include a sensing zone (26)containing a graphene layer (30) so as to form a graphene FET (gFET)array (1). As herein described, the gFET array (1) can be employed tofacilitate nucleic acid hybridization and/or sequencing techniques, suchas based on monitoring changes in hydrogen ion concentration (pH),changes in other analyte concentrations, and/or binding eventsassociated with chemical processes relating to DNA synthesis and/orhybridization reactions, such as within the gated sensing chamber orwell (38) of the gFET based sensor (1). For example, the ChemFET (1) maybe configured as an array of ChemFET sensors and/or may be adapted toincrease the measurement sensitivity and/or accuracy of the sensor(s)and/or associated array(s), such as by including one or more surfaces(26) or wells (38) having a surface layered with a 1D and/or 2Dnanomaterial (30), such as graphene, a dielectric or sensing layer (34),a passivation layer (36), and the like.

For instance, in a particular example, illustrated in FIG. 15A or 15B, achemically-sensitive graphene field effect transistor (gFET) (1), suchas a gFET having a ChemFET structure is provided, where the gFET sensor,e.g., biosensor, may be configured as a ChemFET sensor IC chip, having aplurality of wells (38) configured therein. In such an instance, the ICchip (50) may include a silicon base layer (10) within which the circuitcomponents included of semiconductor, e.g., CMOS, transistors may beembedded. A dielectric layer (20), which may be a silicon dioxide layer,may be included, such as where the silicon dioxide layer is embeddedwith a plurality of conductive sources (22) and conductive drains (24)that are separated from one another so as to form a plurality of channelregions used as sensing regions (26). In particular instances, thechannel regions are configured as a plurality of sensing zones (26),wherein each sensing zone may be contained within a well structure (38).In such an instance, the ChemFET IC chip (50) may include a plurality ofchannel regions (30) that are configured to be solution gated.

Particularly, in various examples, each sensor of the plurality ofsensors includes a ChemFET, e.g., a gFET. For instance, FIG. 2C depictsa top plane view of a first example of a ChemFET (1) having a sensingregion (26) that is surrounded by a well structure (38), wherein thesensing region (26) includes a nanomaterial channel layer (30), such asa graphene channel layer (30). Visible in the top plane view of FIG. 2Cis the passivation layer material (35) which includes the sidewalls ofthe well structure (38). FIG. 2D depicts a top plane view of anotherexample of the ChemFET (1) having a sensing region (26) that issurrounded by a well structure (38), wherein an analyte orreaction-sensitive layer (34) is deposited or otherwise positioned overthe nanomaterial channel layer (30), e.g., a graphene layer (30).Visible in the top plane view of FIG. 2D is the passivation layermaterial (35) which includes the sidewalls of the well structure (38).

FIG. 15A depicts a top plan view of an array of ChemFETs arranged on aChemFET sensor IC chip (50) for a system for analysis of biological orchemical materials or reactions or biologic activity. In variousinstances, the ChemFET sensor IC chip (50) may include a plurality ofChemFET sensors (such as arranged in an array), well structures (38) orpassivation openings associated with the ChemFET sensors and one or morereference electrodes (66) arranged on the chip surface, such as aplatinum or Ag/AgCl reference electrode. FIG. 15B is a side section viewthat depicts a portion of the wells of the array of FIG. 15A in greaterdetail.

In various examples, one or more of the wells (38) may include agraphene-layered surface (30), which in various instances may furtherinclude one or more oxide (34) and/or passivation (35) layers, such aslayers that are disposed on the surface(s) of the bounding members ofthe wells or chambers (37) so as to increase the measurement sensitivityand/or accuracy of the sensors and/or associated array(s). Like above,in such instances, the solution gated chambers (37) of the arrays of theChemFET device may be configured as an ISFET, and be adapted forreceiving the reactants necessary for performing various analyses ofbiological and/or chemical materials, for instance, one or morehybridization and/or sequencing reactions.

Accordingly, in one aspect, a system is provided, such as a systemconfigured for running one or more reactions on biological and/orchemical materials so as to detect a presence and/or concentrationchange of various analyte types, a chemical reaction or biologicactivity in a wide variety of chemical and/or biological processes. Forinstance, in some instances, the biological material may be a nucleicacid or other biological molecule, such as a protein, or the like.Hence, in particular instances, the system may be adapted for performinga DNA hybridization and/or sequencing reaction. In other instances, theanalysis to be performed is for whole genome analysis, genome typinganalysis, microarray analysis, panel analysis, exome analysis,microbial/microbiome analysis, genotyping analysis, and/or clinicalanalysis, such as cancer analysis, NIPT analysis, cfDNA,blood/plasma/serum analysis, and/or UCS analysis.

As such, the system may include an array (130) including one or more,e.g., a plurality of sensors, such as where each of the sensors includesor is otherwise associated with a ChemFET having a conductive source(22), a conductive drain (24), and a sensing surface or channel (30)extending from the conductive source (22) to the conductive drain (24).In particular instances, the array (130) may include one or more wells(38) configured as one or more sensing chambers (37) having the sensingsurface or channel (30) positioned therein. In some instances, thesurface and/or channel (30) of the chamber (37) may include aone-dimensional (1D) or two-dimensional (2D) nanomaterial (30), adielectric or sensing layer (34), a passivation layer (35), and/or thelike.

As can be seen with respect to FIG. 15C, the system (100) may include afluidics component (120) for directing and controlling the flow ofvarious fluids throughout the system (100). The fluidics component (120)may be used for various purposes, such as for use in performing thereaction, e.g., delivering one or more analyte containing solutions tothe sensor array (130) for the performance of the reaction thereby, acircuitry component (140), such as for running the reaction and/ordetection processes, and/or a computing component (150), such as forcontrolling and/or processing the same. For instance, a fluidicscomponent (120) may be included where the fluidic component isconfigured to control one or more flows of analytes and/or reagents overthe array (130) and/or one or more chambers thereof.

Particularly, in various examples, the system (100) includes a pluralityof sensing locations, such as sensing regions (26) and/or wells (38),which in turn includes a plurality of sensors and/or a plurality ofchannels, and further includes one or more fluid sources (120), e.g.,containing a fluid having a plurality of reagents and/or analytestherein, and fluid conduits, such as for delivery of the fluids from thesource (120) to the one or more sensing regions (26) and/or wells (38)of the sensor array (130) for the performance of one or more reactionsthereby. In certain instances, a mechanism for generating one or moreelectric and/or magnetic fields is also included.

As can be seen with respect to FIG. 15D, the system (100) mayadditionally include a circuitry component (140), such as where thecircuitry component may include an address decoder (144), a sampleand/or hold circuit (143), a bias circuitry (142), and/or at least oneanalog-to-digital converter (141). For instance, the address decoder(144) may be configured to create a column and/or row address for eachsensor of the array (130), such as by associating a unique identifierwith each sensor, such as based upon its location within a given row andcolumn within the array (130). It may also be configured for inputtingor otherwise directing the various operations that rely upon theaddressing of operations for a given well of the array. For instance,the address decoder (144) may target select signals to specific wells(38) based on their column and/or row identifiers, so as to access asensor and/or direct fluid flow to a given location, e.g., addresswithin the array (130).

The sample and hold circuit (143) may be configured to hold an analogvalue of a voltage to be applied to or on a selected well or columnand/or row line of an array (130) of a device of the disclosure, such asduring a read interval. Likewise, the bias circuitry (142) may becoupled to one or more surfaces and/or chambers of the array (130) andmay include a biasing component such as may be adapted to apply a readand/or bias voltage to selected ChemFETs of the array (130), e.g., suchas to a gate terminal of the transistor. The analog to digital converter(141) may be configured to convert an analog value to a digital value(142), for instance, as a result and/or output of the reaction within anidentified well (35) or selection of wells, e.g., a line of columns androws.

Additionally, as can be seen with respect to FIG. 15E, a computingcomponent (150) may also be included, such as where the computingcomponent (150) may include one or more processors, such as a signalprocessor (151), a base calling module (52), and a mapping, alignment,and variant calling module (153) and a processor (154). The signalprocessor (151) may be configured for determining one or more bases ofone or more reads of a sequenced nucleic acid, such as results from asequencing reaction. The base caller of the base calling module (152)may be configured to correct a plurality of signals, such as for phaseand signal loss, to normalize to a key, and/or to a generate a pluralityof corrected base calls for each flow in each sensor to produce aplurality of sequencing reads.

The mapping, alignment, and variant calling module (153) may beconfigured for performing one or more analytics functions on thesequenced data, and may include one or more of a mapping module,configured for generating one or more seeds from the one or more readsof sequenced data and for performing a mapping function on the one ormore seeds and/or reads; an alignment module, configured for performingan alignment function on the one or more mapped reads; a sorting module,configured for performing a sorting function on the one or more mappedand/or aligned reads; and/or an variant calling module, configured forperforming a variant call function on the one or more mapped, aligned,and/or sorted reads. The processor (154) may be a general-purposeprocessor or a processor specialized for tasks other than thoseperformed by the signal processor (151). In various examples, the deviceand/or system may include at least one reference electrode.

The system and its components may be implemented wholly on the ChemFETsensor IC chip (50) with the circuitry to support those componentsprovided by the semiconductor transistors, e.g., CMOS transistors, orthe system may be partially implemented on the ChemFET sensor IC chip(50) and partially on a separate system device (not shown). For example,the ChemFET sensor IC chip (50) may include the circuitry component(140) that may include ROIC circuitry as well as the ChemFET sensorarray (130) and the separate system device may include most of theFluidics component (120) and all of the computing component (150).

Particularly, the system can be configured for performing a nucleic acidhybridization or sequencing reaction. In such examples, the device forperforming the hybridization or sequencing reaction may be adapted fromCMOS circuitry and structures adapted to include one or more sensingchambers (37), e.g., micro or nano-wells (38), so as to form an array(130). The array (130) may be associated with one or more sensors havingone or more ChemFETs (1) linked therewith. Such CMOS transistors mayinclude a cascode transistor having one or more of a source terminal, adrain terminal, and or a gate terminal, while the ChemFETs (1) are usedto form sensing zones. In such an instance, the source terminal of thecascode transistor may be directly or indirectly connected to the drainterminal of the ChemFET.

In some instances, the gate terminal may couple to or may otherwisecontrol or influence the ChemFET channel (30), and such channel mayfurther include a 1D or 2D nanomaterial. The 1D or 2D nanomaterial mayextend from the source terminal (22) to the drain terminal (24), such aswhere the 1D channel nanomaterial may be a carbon nanotube orsemiconductor nanowire, and the 2D channel nanomaterial is composed ofgraphene, silicene, a phosphorene, a molybdenum disulfide, a metaldichalcogenide or other 2D nanomaterial. The device may further beconfigured to include a plurality of arrays, such as arranged as one ormore lines of columns and rows coupled to the sensors in the array ofsensors. In such an instance, each column line in the plurality ofcolumn lines may be directly or indirectly connected to or otherwise becoupled with the drain terminals of the transistors, e.g., cascodetransistors, of a corresponding plurality of sensors or pixels in thearray, and likewise each row line in the plurality of row lines may bedirectly or indirectly connected to or otherwise coupled with the sourceterminals of the transistors, e.g., cascode transistors, of acorresponding plurality of sensors in the array.

In some instances, a plurality of source and drain terminals having aplurality of channel members and/or associated sensing surfaces,extended there between may be included, such as where each channelmember includes a one- or two-dimensional nanomaterial. In such aninstance, a plurality of first and/or second conductive lines may becoupled to the first and second source/drain terminals of the ChemFETsin respective columns and rows in the array. Additionally, controlcircuitry (140) may be provided and coupled to the plurality of columnand row lines such as for reading a selected sensor connected to aselected column line and/or a selected row line.

The circuitry may also include a biasing component (142) such as may beconfigured for applying a read voltage to the selected row line, and/orto apply a bias voltage such as to the gate terminal of a transistor,such as FET and/or cascode transistor of the selected sensor. In aparticular example, the bias circuitry (142) may be coupled to one ormore chambers of the array (130) and be configured to apply a read biasto selected ChemFETs via the conductive column and/or row lines.Particularly, the bias circuitry (142) may be configured to apply a readvoltage to the selected row line, and/or to apply a bias voltage to thegate terminal of the transistor, e.g., cascode transistor, such asduring a read interval.

Sense circuitry can be included and coupled to the array so as to sensea charge coupled to one or more of the gate configurations of a selectedChemFET. Sense circuitry can be configured to read the selected sensorbased on a sampled voltage level on the selected row and/or column line.In such an instance, the sense circuitry may include one or more of apre-charge circuit, such as to pre-charge the selected column line to apre-charge voltage level prior to the read interval; and a samplecircuit such as to sample a voltage level at the drain terminal of theselected transistor, e.g., cascode transistor, such as during the readinterval. The sample circuit may also be included and contain a sampleand hold circuit (143) configured to hold an analog value of a voltageon the selected column line during the read interval, and may furtherinclude an analog to digital converter (141) to convert the analog valueto a digital value.

Control of Microbead Loading in Wells

In some instances, it may be useful to provide a mechanism for assistingthe targeting of the microbead(s) (60) to the sensing zone (26) of theChemFET (1). Particularly, as can be seen with respect to FIGS. 5A-E, aChemFET (1) is provided. In this instance, the transistor (1) may be amulti-layered structure including a primary, e.g., a substrate layer 10,a secondary structure layer, e.g., a dielectric layer 20, and mayfurther include an additional passivation layer 35, e.g., a silicondioxide layer, which layer may be cavitated so as to include a divot(38), such as a divot on a surface (21) of the substrate, and sized toat least partially contain a nano- or microbead (60) therein.

In certain instances, the surface of the divot (38) may be centered suchthat the bead (60) rests within the divot (38) so as to be proximate thesensing zone (26) and/or a channel structure (30) associated therewith.In particular instances, the sensing zone (26) includes a graphene layer(30) positioned at least partially between the primary and tertiarylayers, and in such instances, an analyte or reaction-sensitive layer(34) may be positioned above the graphene layer within the sensing zone(26). In this instance, to draw and/or attach the bead(s) (60) to thesensing zone (26), an electromagnetic field may be employed. Hence, asshown in FIG. 19A, a microbead (60) is positioned on the transistorsurface 21, within the sensing zone (26), and in proximity to a channel(30).

More particularly, the sensing zone (26) of the ChemFET (1) may beconfigured to include a channel (30) that is formed to correspond to theregion, and create a point of contact or proximity between the surfaceof the graphene layer (30) and the bead (60). Further, to facilitatethis contact or proximity, the ChemFET (1) may include an attractingmechanism (70) that is configured to attract or otherwise draw the bead(60) into proximity of the sensing zone (26) and/or channel (30). Forinstance, in particular instances, the nano- or microbead (60) mayinclude a charged and/or metallic element, and the attracting mechanism(70) may be configured so as to generate an electric and/or magneticfield, such as for drawing the microbead (60) to the sensing zone (26).For example, in some examples, the electric field generator (70) may bea pulse generator, and in other examples, such as illustrated in FIG.19A, the magnetic field generator (70) may be a magnet.

Particularly, as shown in FIG. 19A, one or more nano- or microbeads (60)of the disclosure may be configured for facilitating the performance ofa bio-chemical reaction such as on a sensing region (26) of the ChemFET(1). For instance, in particular examples, each of the one or moremicrobeads (60) may include a biological material or a chemicalmaterial, associated therewith. In such an instance, the microbead (60)may be introduced to the region (26) of the ChemFET (1) of the system,such as for nucleic acid sequencing, in such a manner that it is drawnor otherwise attracted to the region (26), such as by electromagnetism.

For instance, the microbead (60) may be configured to include electriccharge and/or paramagnetic properties so as to assist it in being drawninto proximity of a sensing location (26) positioned on a surface (21)of the ChemFET (1), such as where the nucleic acid sequencing reactionmay take place. Hence, the device may include an electro-magnetic fieldgenerating component (70) that is configured to apply anelectro-magnetic field that is focused within the sensing zone (26) soas to interact with the electric charge and/or paramagnetic propertiesof the microbead (60) thereby drawing it into proximity of the surface(21) and/or into the sensing zone (26), such as via electro-magnetism.In this instance, the layers and other components of the ChemFET (1) areconfigured in such a manner that the sensing zone (26) need not includebounding members, or if included the bounding members may be thin,allowing for a higher density of wells on the array.

Alternatively, in other examples, such as presented in FIG. 19B, theChemFET(1) may include a well structure (38) that is configured forreceiving one or more nano- or microbeads (60), such as for nucleic acidsequencing therein. For instance, each of the one or more microbeadsincludes an analyte and/or reactant, which is configured forparticipating in a reaction, such as a nucleic acid hybridization and/orsequencing reaction. Accordingly, the ChemFET (1) may include a sensinglocation (26) that may be configured as a surface within a well (38) ofthe ChemFET (1), such as where the sensing location (26) is proximate achannel (30) of the ChemFET (1). The nano- or microbead (60) may beconfigured for use in a system for analysis of biological and/orchemical materials such as on or within a sensing surface (26), such aswithin a well (38) of the ChemFET (1). In this and other instances, themicrobead (60) may be introduced to the surface (21) of the ChemFET (1)of the system in such a manner that it is drawn or otherwise attractedtoward the sensing surface (26), e.g., of a well structure (38), wherethe nucleic acid sequencing reaction may take place, such as byelectro-magnetism.

For example, the microbead (60) may be configured to have an electriccharge property and the microbead attracting mechanism (60) may beconfigured to emit an electric field that is opposite in nature to thecharge on the microbead and is thereby adapted for draw the microbead(60) into proximity of the sensing surface (26). In such an instance, anelectric field component generates an electric field to interact withthe electric charge properties of the microbead. Hence, the microbeadmay be drawn to the sensing location using electrophoresis. In otherinstances, the microbead (60) may be configured to include paramagneticproperties so as to assist it in being drawn or otherwise attractedtoward sensing surface (26), e.g., into the well (38), and intoproximity of the sensing zone, where the reaction may take place.

The device, therefore, may include a magnetic field generating component(70) that is configured to apply an electro-magnetic field that isfocused within the chamber (38) so as to interact with the paramagneticproperties of the microbead (60) thereby drawing it into the chamber(38) and/or proximate the sensing surface (26), such as via magnetism.Particularly, in various examples, the microbead or particle attractingmechanism (60) can be configured to emit a magnetic field that isopposite in polarity to the paramagnetic properties of the microbead andis thereby adapted for draw the microbead (60) into proximity of thesensing surface (26). In such an instance, a magnetic field componentgenerates a magnetic field to interact with the polar properties of themicrobead. The use of magnetism and/or electrophoresis allows forthinner sensing location structures.

Additionally, as illustrated in FIG. 19B, in some examples, the systemand its components may be configured such that when the electromagneticfield is generated it interacts with the microbead (60) and/or acomponent associated therewith so as to pull the microbead toward thesensing zone (26). In other examples, as illustrated in FIG. 19C, thesystem and its components may be configured such that when theelectromagnetic field is generated it interacts with the components ofthe microbead (60) so as to push the microbead away from the sensingzone (26). Accordingly, the electromagnetic fields can be generatedand/or reversed so as to attract or repulse the nano-/micro-bead to orfrom the sensing location (26), such as to or away from a well (38), andthus utilizing an electronic and/or magnetic field, the nano- ormicrobead may be positioned within the device, such as within a wellthereof.

As illustrated in FIG. 19D a ChemFET (1) is provided, such as for asystem for analysis of biological and/or chemical materials, such as byutilizing an electric and/or magnetic field generating mechanism such asfor positioning of a nano- or microbead (60) in relation to the sensingsurface (26). For instance, in particular instances, a voltage may beapplied between a location above the solution of the solution gate (37)and a location on or below the sensing location (26), such as above thepackage lid (47) and/or below a metal component, e.g., a plate, belowthe package (not shown). In certain instances, the location below thesensing location (26) may include a metal or other conductive layer suchas within the package or package substrate. Hence, in various instances,the field generating mechanism (70) may be employed to generate and/orreverse an electric or magnetic field so as to insert or eject one ormore microbeads from one or more wells, sensors, and/or channelsassociated therewith, either entirely or selectively.

Particularly, as set forth in FIG. 19E, a ChemFET sensor IC chip (50)included of ChemFETs (1) for a system for analysis of biological orchemical materials is provided. The ChemFET sensor IC chip (50) includesa multiplicity of wells (38) each forming a sensing location (26)whereon a bio-chemical reaction may take place. Additionally, eachsensing location (26) is associated with a field generator (70), e.g., amagnet, which is configured so as allow for the selective filling of thesensing locations (26) with one or more types of nano- or microbeads(60). Accordingly, by utilizing multiple field generators (70), e.g.,multiple magnets, for generating a plurality of electro-magnetic fields,the nano- or microbeads (60) may be positioned within the pluralitywells (38). Such positioning may be selective such as by selecting whichgenerators will be on, off, or reversed, so as to fill or not fill theirrespective wells (38), as desired. In various examples, theelectromagnetic fields for any given well (38) may be reversed so as toexpel a microbead (60) from the well (38) and/or sensing zone (26).

Particularly, in a further aspect of the present disclosure, a systemhaving an array of ChemFETs including a plurality of chambers (37)having well structures formed therein is provided. In such an instance,the wells (38) may be structured as or may otherwise include sensinglocations (26) wherein one or more chemical reactions may take place. Insuch an example, the system may include one or more fluidics componentshaving one or more fluid sources, e.g., reservoirs, containing one ormore fluids therein and configured for delivering the fluid from thereservoir to the sensing chamber (37), such as for the detection of abiologic and/or the performance of one or more chemical and/orbiological reactions, such as a nucleic acid sequencing reaction.Accordingly, the fluidics component, e.g., the fluid source, may be influidic communication with the FET device configured for biologicaland/or chemical analysis, and may be configured for controlling a flowof reagents over the array.

Accordingly, in certain instances, the fluid may include one or morereactants, such as one or more analytes necessary for performing anucleic acid hybridization sequencing reaction, as herein described. Ina particular example, the fluid may include one or more, e.g., aplurality of microbeads (60), having a nucleic acid template (65)attached thereto, for instance, where the template is a DNA or RNAmolecule to be sequenced, and the fluid containing the microbead (60) isto be delivered to the well (38) such as for carrying out the sequencingreaction. In such an example, one or more of, e.g., each, of theplurality of microbeads may be configured so as to have electric chargeand/or paramagnetic properties.

The device may additionally include an electric and/or magnetic fieldcomponent (70), e.g., having an electric and/or magnetic fieldgenerator, such as where the electric and/or magnetic field component(70) is configured to generate an electric and/or magnetic field so asto interact with the electric and/or magnetic charge properties of eachof the plurality of microbeads (60) to attract the microbeads into asensing location, such as a sensing surface, a channel, a well, achamber, and/or a sensor of the FET device, such as by usingelectrophoresis and/or magnetism.

Hence, one or more, e.g., a plurality of microbeads (60), may be drawnonto or into a sensing location (26) of the plurality of sensinglocations (26), which locations may be formed as wells (38), e.g., oneor more thin wells. The use of magnetism or electrophoresis allows forthinner sensing location structures. In particular instances, anelectric and/or magnetic field generator (70) may be configured fordrawing and/or positioning the microbeads within the well structure(38), such as in proximity to a channel (30) or chamber (37) of thedevice, and in other instances, the electric and/or magnetic fieldgenerator (70) may be configured for reversing the electrical and/ormagnetic field so as to repulse the microbead(s) (60) from the sensinglocation (26), channel (30), and/or chamber (37). In various instances,an array of sensing locations (26) may be provided each having a magnet(70) that allows for selective filling of the sensing locations withdifferent numbers and/or types of microbeads (60), such as at selectsensing locations (26). In such an instance, multiple electric and/ormagnetic field generators for selective filling of sensing locations,e.g., wells.

Accordingly, one aspect of the present disclosure is a system and/or amethod for positioning one or more, e.g., a plurality, of microbeads(60) within a sensing or plurality of sensing locations (26) forbiological or chemical analysis, such as for nucleic acid sequencing.The system may include a ChemFET sensor IC chip (50) having anintegrated circuit structure configured for performing a biological orchemical analysis, such as within a plurality of nano- or micro-sensingwells (38), as described above, having a fluidic component (120), acircuitry component (140), and/or a computing component (150) and themethod may include one or more of the following steps. For instance, themethod may include the fluidic component (120) introducing a fluid to bein contact with the ChemFET sensor IC chip (50), such as where thefluidics component is configured to control a flow a fluid of reagentsover the ChemFET sensor IC chip (50), and the fluid may include one ormore microbeads (60) that may have electric charge and/or paramagneticproperties.

In such an instance, the ChemFET sensor IC chip (50), may include anintegrated circuit structure, a plurality of sensing locations (26)having one or more wells (38), a plurality of ChemFET sensors (1) and/ora plurality of channels (30), and/or an electric and/or magnetic fieldcomponent (70). The electric field and/or magnetic field component (70)may be configured to activate the electronic and/or magnetic field, andthe method may also include activating an electric and/or magnetic fieldso as to interact with the electric and/or paramagnetic properties ofeach of the microbeads (60). The method may additionally include drawingthe one or more microbeads (60) into proximity with a sensing zone (26)of the plurality of sensing locations (37) using electrophoresis and/ormagnetism. In certain instances, the method may include positioning theone or more microbeads (60) within the one or more sensing locations(37) for biological or chemical analysis.

In particular instances, the electric and/or magnetic fields may begenerated by the plurality of electric and/or magnetic field generators(70), e.g., included in the integrated circuit structure of the ChemFETsensor IC chip (50), in all or only a subset of the plurality of sensinglocations (37) so as to only attract a plurality of microbeads (60) tothe subset of sensing locations, such as for selectively filling theplurality of sensing locations (37) with the plurality of microbeads(60). In such an instance, different types of microbeads (60) may beattracted to different sensing locations, such as by pulsing the voltageand/or magnetic generators and/or keeping the same constant.

Particularly, where an electric field generator (70) is provided thevoltage applied to the ChemFET sensor IC chip (50), may be variable orconstant and may be less than about 10V, such as about less than 8V, orless than about 6V, including less than about 4V or about 2V or 1V. Thevoltage may be applied between a location above the fluid (47) and alocation on or below the sensing zone (26), such as above the packagelid and/or below the metal plate below the package. In certaininstances, the location below the sensing location may be a metal orconductive layer such as within the package or package substrate. Themethod may also include the step of reversing the electric or magneticfield so as to eject the plurality of beads from the plurality of wells,sensors, and/or channels, either entirely or selectively.

Further, as indicated, each or a subset of the plurality of sensinglocations (26) may be utilized to generate electric fields to attract amicrobead (60) thereby allowing for programmability to each or a subsetof sensing locations (26), for instance, 99% or 95% or 90% or 85%, or80% or less of the plurality of wells (38) are occupied with a microbead(60). Hence, the electric and/or magnetic field may be generated in onlya subset of the plurality of wells (38), sensor regions (26) or channels(30) to only attract a plurality of microbeads (60) to the subset.Likewise, a plurality of electric and/or magnetic field generators (70)for selective filling the plurality of wells (38), sensor locations (26)or channels (30) with the plurality of microbeads (60), and/or ejectingthe plurality of microbeads (60) from the plurality of wells (38),sensor locations (26) or channels (30). In such an instance, theelectric and/or magnetic field generator (70) may be an electric source,a permanent magnet and/or an electromagnet. As indicated, the pluralityof magnetic field generators (70) is configured to reverse the magneticfield to eject the plurality of microbeads (60) from the plurality ofsensing locations (37) or a subset thereof.

Additionally, in one aspect of the present disclosure, a device, system,and/or method for verifying well occupancy for a plurality of wells (38)for analysis of biological or chemical materials may be provided. Thesystem may include a device for receiving a fluid containing theplurality of microbeads (60). Particularly, the ChemFET sensor IC chip(50) may include a processor, a CMOS structure having an integratedcircuit, a plurality of wells (38), and a plurality of ChemFET sensors(1).

Each of plurality of wells (38) may be configured to receive a microbead(60) of the plurality of microbeads, and the ChemFET sensor IC chip(50), may include a mechanism (70) for drawing and/or ejecting themicrobeads (60) into or out of the wells (38). Hence, the method mayinclude the step of flowing the plurality of microbeads (60) over and/orinto the plurality of sensing locations (26/37) and/or wells (38) and/ormay include determining, e.g., through electrical and/or magneticsensing if a sensing location (26/37) and/or well (38) is occupied orunoccupied by a microbead (60) and/or if a location (26/37) contains oneor multiple microbeads (60).

Consequently, the processor (154) may be configured to determine if awell (38) is unoccupied and/or if the well (38) contains one or more,e.g., multiple microbeads (60). In certain instances, the processor(154) may also be configured to eliminate or modify one or more of themeasurements, such as based on the number of wells (38) occupied orunoccupied, e.g., the number of wells (38) containing none, one ormultiple microbeads (60). For instance, the processor (154) may beconfigured to eliminate from the measurement the number of wellsunoccupied and the number of wells containing multiple microbeads (60),or compensate in the measurement for the number of wells (38) unoccupiedand the number of wells (38) containing multiple microbeads (60), andthe like. In such instances, the measurement may be a shift in an I-V orI_(d)-V_(gs) curve (or a parameter thereof), as explained below. Inparticular instances, the processor (154) may be configured to eliminatefrom the measurement the number of wells (38) unoccupied and the numberof wells (38) containing one or multiple microbeads (60) and/or tocompensate in the measurement for the number of wells (38) unoccupiedand the number of wells (38) containing one or multiple microbeads (60).Accordingly, in some examples, the measurement may be a shift in an I-Vor I_(d)-V_(gs) curve, such as one or more of: generating a plurality ofI-V or I_(d)-V_(gs) curves so as to determine a shift in response to achemical reaction occurring on or near the ChemFET; generating a ChemFETI-V or I_(d)-V_(gs) curve in response to a chemical reaction occurringon or near the ChemFET so as to detect a change in the slope of the I-Vcurve; and/or to sense shifts in a capacitance as a function of a gatevoltage.

Graphene Growth

For instance, in particular examples, improved fabrication techniquesfor producing a CMOS sensor device containing sensing zones employing a1D or 2D nanomaterial layer are provided. Specifically, in certaininstances, a 1D or 2D nanomaterial layer may be grown, such as on agrowth platform, and once grown may be released from the growthplatform, and then be transferred to a semiconductor structure, such aCMOS substrate, so as to be employed as a sensor device as hereindescribed. In particular examples, the 1D nanomaterial may be a carbonnanotube or a semiconductor nanowire, e.g., grown on a substrate, and inother examples, the 2D nanomaterial may be graphene, silicene,molybdenum disulfide, black phosphorous (phosphorene), borophene,tungsten disulfide, boron nitride, tungsten diselenide, stanene,germanane, nickel HITP, and/or metal dichalcogenides or Mxenes such asTi2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2, Ti3CN, Nb4C3, or Ta4C3.

There are several growth mechanisms that may be implemented for thegrowth of the 1D or 2D nanomaterial on a substrate. In certaininstances, the growth substrate may be a metal plate, a metal foil, orother thin film metal, such as a metal positioned on or over a wafer,such as a silicon wafer. The 1D or 2D nanomaterial may be deposited onthe growth substrate, such as for growing, by any suitable mechanism,such as by chemical vapor deposition (“CVD”) (atmospheric, low, or verylow pressure), PECVD, ALD, submergence within a hot wall or cold wallreactor, and the like.

Graphene Transfer

There are several transfer mechanisms for transferring the growing orgrown 1D or 2D structure to a substrate, such as a substrate containingan integrated circuit, such as by direct transfer from the growthsubstrate to the wafer, e.g., a ROIC (Read-out Integrated Circuit)/CMOSwafer, such as by using Van der Waal's forces, fusion bonding, or othersuitable form of temporary bonding. Additionally, there are severalrelease mechanisms for effectuating the release of the 1D or 2Dnanomaterial from the growth substrate and the attachment to the ROICwafer, including aqueous electrolyte electrolysis, where the growthplatform acts as the cathode and separation is produced due to hydrogenevolution. Another release mechanism may include separation caused byuse of a temporary adhesive from the growth platform, and/or by use of alaser, a UV light, a temperature increase, or physical peeling orpulling.

Particularly, a direct transfer method is set forth as FIG. 22. Forinstance, in an exemplary sequence of steps, a growth substrate isprovided. A graphene layer may then be deposited on to the growthsubstrate, such as by a chemical vapor deposition (CVD) process.Likewise, a ROIC/CMOS wafer may be provided, such as in opposedrelationship to the graphene containing substrate. Further, a releaseand transfer step may take place, such as where the graphene is releasedfrom the growth substrate and transferred onto the CMOS wafer. Thegraphene layer may then be patterned and one or more interconnectsand/or wells may be deposited and/or patterned. The composition may thenbe tested, such as with respect to sensor operation of the underlyingintegrated circuit. The chip may then be assembled into a package, and apackage level test may occur, and once passed the chip set may beshipped.

More particularly, an effective method for producing such a transfer,e.g., involving a Van Der Waals Bond transfer mechanism, is illustratedin FIGS. 22A-22F. In FIG. 22A, the 2D nanomaterial, e.g., graphene, isgrown on a growth platform such as composed of a thin metal layer, e.g.,silver, ruthenium, copper, or platinum layer, that is positioned on agrowth wafer. In FIG. 22B, the orientation of the growth platform isflipped with respect to its fabrication process. In FIG. 22C, a siliconROIC/CMOS wafer containing a suitably configured oxide layer, e.g.,silicon dioxide, is prepared, and the flipped growth platform and thesilicon wafer are aligned for bonding. In FIG. 22D, the 2D nanomaterialon the growth platform is bonded to the oxide layer, e.g., silicondioxide layer, on the ROIC wafer using Van der Waals forces. FIG. 22Eshows the use of water electrolysis to create hydrogen bubbles toseparate the 2D nanomaterial from the metallized growth platform, whichacts as a cathode in such a water electrolysis reaction. In FIG. 22F,the growth substrate is removed, leaving the 2D nanomaterial on theROIC/CMOS wafer.

FIGS. 26A-26F also depicts the same steps of direct bond transfer viaVan der Waals forces as in FIGS. 22A-22F, with the distinction thatFIGS. 26A-26F show the growth platform is patterned to create one ormore channels or divots that allow for better water access and moreefficient bubble transfer. Such openings may later be converted into oneor more well or chamber boundaries as herein described.

FIGS. 27 and 28 illustrate an alternative method for the above-describedbubble elution and/or release mechanism as illustrated with respect toFIGS. 26 and 22, For instance, FIG. 27 depicts graphene transfer using amodified Langmuir-Blodgett trough. As shown in FIG. 28A, a structurecomposed of a PMMA substrate, a 2D nanomaterial, e.g., graphene, copper,and a base layer is subjected to a controlled immersion within thetrough and subjected to a bubble release protocol. As shown in FIG. 28B,the 2D nanomaterial and the PMMA substrate are fully released from thecopper structure. As shown in FIG. 28C, the solution is drained in sucha manner that the 2D nanomaterial is aligned with and becomes bonded toa target wafer, e.g., a silicon CMOS wafer, so as to transfer the 2Dnanomaterial layer onto the target wafer.

FIG. 21 shows a flow chart of a general method of forming asemiconductor wafer with transistors having 2D nanomaterial layers. Akey process step is the transfer of the 2D nanomaterial, such asgraphene, from a growth substrate to the target substrate, such as aROIC wafer. Discussed elsewhere are a variety of different transfertechniques that generally use some release method to release thegraphene from its growth substrate and a temporary bonding method, suchas adhesive bonding of the graphene to a carrier and then Van der Waalsbonding of the graphene to the target wafer with a subsequent secondrelease step, such as by thermal, laser or UV energy to release theadhesive and carrier wafer from the graphene. These transfer processesthat require temporary bonding and direct or indirect contact to thegraphene layer are not optimal as they open many opportunities fordefects in the graphene. A preferred approach uses direct transferfusion bonding of oxide, such as silicon dioxide layers, as illustratedin FIGS. 23A-23F.

FIGS. 23A-23F visually show the steps of direct bond transfer via fusionbonding. In the direct transfer fusion bonding process, the 2Dnanomaterial (530), e.g., graphene, is encapsulated with SiO2 (520)while it is still on the growth wafer and then the growth wafer may befusion bonded to a properly prepared CMOS ROIC wafer. Platinum,ruthenium, silver, copper, or another suitable metal may be used forgrowing the 2D nanomaterial (530) on the growth substrate. A release orseparation mechanism (e.g., bubble process) is used to separate the 2Dnanomaterial (530) from the platinum or other metal (528). The growthwafer may be a silicon, sapphire (Al2O3), or other suitable substratecapable of sustaining high temperatures with low thermal expansion.

In FIG. 23A, the 2D nanomaterial (530), preferably graphene, is grown ona growth platform included of a platinum layer (528) on a growth wafer(510).

In FIG. 23B, a cover material of silicon oxide is deposited on the 2Dnanomaterial and then the oxide is polished or CMP'ed to provide a veryflat and smooth surface on the silicon oxide.

In FIG. 23C, the growth platform is flipped.

In FIG. 23D, a ROIC wafer is prepared by polishing or CMP'ing a topmostsilicon oxide layer to provide a very flat and smooth surface on thesilicon oxide. The ROIC wafer and the growth platform are aligned forbonding.

In FIG. 23E, the silicon oxide cover material (520) is bonded to theROIC wafer topmost silicon oxide layer (520) through a fusion bondingprocess.

In FIG. 23F, the growth substrate is separated from the ROIC wafer,leaving the 2D nanomaterial (530), preferably graphene, on the ROICwafer, i.e., the process effectively transfers the 2D nanomaterial fromthe growth substrate to the ROIC wafer via fusion bonding. In the directtransfer fusion bonding process, the 2D nanomaterial, preferablygraphene, is encapsulated with SiO2 effectively protecting it fromhandling and process damage, and then the growth wafer is fusion-bondedto a CMOS ROIC wafer.

Platinum, copper, or another suitable metal is used for growing the 2Dnanomaterial (530). A release or separation process (e.g., a bubbleprocess) is used to separate the 2D nanomaterial (530) from the platinumor other metal (528). The growth wafer is preferably silicon, sapphire(Al2O3), or another suitable substrate capable of sustaining hightemperatures with low thermal expansion. Alternatively, a wafer formatis replaced with a panel or sheet. Various encapsulating materials areutilized such as SiO2, Si, Si3N4.

FIGS. 24A-24H show a variation the fusion bonding process, in this caseusing the process to first coat the graphene with an analyte orreaction-sensitive layer, such as an ion sensitive oxide layer, and thenbonding this ion sensitive oxide layer to a carrier wafer. Releasing thegraphene from the growth substrate and fusion bonding are similar to thepreviously described process, but the resultant final structure isdifferent since the ion sensitive oxide layer is integral to the finallayer stack—thus both the graphene layer and the ion sensitive oxidelayer are transferred by fusion bonding using this process.

In FIG. 24A, the 2D nanomaterial (530), preferably graphene, is grown ona growth platform included of a platinum layer (528) on a growth wafer(510).

In FIG. 24B, an ion sensitive oxide material is deposited on the 2Dnanomaterial.

In FIG. 24C the ion sensitive oxide is releasably joined to a carrierwafer.

In FIG. 24D the growth substrate has been removed (e.g., by a bubblerelease process or other means) exposing the graphene.

In FIG. 24E, a cover material of silicon oxide is deposited on the 2Dnanomaterial and then the oxide is polished or CMP'ed to provide a veryflat and smooth surface on the silicon oxide.

In FIG. 24F, the carrier platform is flipped and aligned with apreviously prepared ROIC wafer (e.g., CMP and/or polished SiO2 surface).

In FIG. 24G, the silicon oxide cover material (520) is bonded to theROIC wafer topmost silicon oxide layer (520) through a fusion bondingprocess.

In FIG. 24H, the carrier is separated from the ROIC wafer, leaving the2D nanomaterial (530), preferably graphene, covered with the ionsensitive layer (on the ROIC wafer, i.e., the process effectivelytransfers the 2D nanomaterial from the growth substrate to the ROICwafer via fusion bonding. In the direct transfer fusion bonding process,the 2D nanomaterial, preferably graphene, is encapsulated with SiO2effectively protecting it from handling and process damage, and then thegrowth wafer is fusion-bonded to a CMOS ROIC wafer.

FIG. 25 shows a wafer undergoing a bubble release process wherebygenerated gas bubbles are intended to gently force the graphene layerfrom its growth substrate. In practice this may be difficult to do sinceit is problematic to contact the thin film used on the growth substrate(it is both thin and covered by graphene). To be make electricallycontacting the growth wafer easier a TSV 43 can bring an electrical pathfrom the thin film on the growth side of the wafer trough the wafer to aconductive layer on the backside of the wafer. It is easy to access thebackside of the wafer for electrical contact

Nanomaterial Layer Transfer by Fusion Bonding

In view of the above, in various examples, FIG. 21 provides a flow chartof a general method of forming a semiconductor wafer with transistorswith a 2D nanomaterial layer in accordance with the methods set forthabove. FIGS. 24A-24F illustrate the various steps. For instance, anexemplary direct transfer mechanism including direct transfer fusionbonding is provided and shown in FIGS. 25A-25F. FIGS. 25A-25F visuallyshow the steps of direct bond transfer via fusion bonding. In FIG. 25A,the 1D or 2D nanomaterial, such as graphene, is grown or deposited on agrowth platform included of a platinum layer on a growth wafer. In FIG.25B, a cover material of silicon oxide is deposited on the 1D or 2Dnanomaterial and then the oxide is polished or CMP'ed to provide a veryflat and smooth surface on the silicon oxide. In FIG. 25C, the growthplatform is flipped. In FIG. 25D, a ROIC wafer is prepared by polishingor CMP'ing a topmost silicon oxide layer to provide a very flat andsmooth surface on the silicon oxide. The ROIC wafer and the growthplatform are aligned for bonding. In FIG. 25E, the silicon oxide covermaterial is bonded to the ROIC wafer topmost silicon oxide layer througha fusion bonding process. In FIG. 25F, the growth substrate is separatedfrom the ROIC wafer, leaving the 1D or 2D nanomaterial on the ROICwafer, i.e., the process effectively transfers the 1D or 2D nanomaterialfrom the growth substrate to the ROIC wafer via fusion bonding.

In the direct transfer fusion bonding process, the 1D or 2Dnanomaterial, e.g., graphene, may be encapsulated with SiO2 and then thegrowth wafer may be fusion bonded to a CMOS ROIC wafer. Platinum, gold,silver, copper, or another suitable metal may be used for growing the 2Dnanomaterial or in the case of 1D nanomaterial it is deposited on thegrowth substrate. A release or separation mechanism (e.g., bubbleprocess) is used to separate the 1D or 2D nanomaterial from the platinumor other metal. The growth wafer may be a silicon, sapphire (Al2O3), orother suitable substrate capable of sustaining high temperatures andthermal expansion. Alternatively, a wafer format may be replaced with apanel or sheet. Various encapsulating materials may be utilized such asSiO2, Si, Si3N4. The same process may also be utilized with othermaterials that can be bonded such as polymers. Alternative methods forgrowing and transferring 2D nanomaterials are disclosed in Hoffman etal., U.S. Provisional Patent Application No. 62/175,351, filed on Jun.14, 2015, for System And Method For Growing And Transferring GrapheneFor Use As A FET, which is hereby incorporated by reference in itsentirety.

FIGS. 29A-29G depict a process for temporary bonding that employs anadhesive material (such as an acrylate) so as to effectuate temporarybonding. In FIG. 29A, a glass carrier including an LTHC and an adhesiveis prepared. In FIG. 29B, the growth platform containing the 2Dnanomaterial, e.g., grown in accordance with the above, is bonded to theglass carrier such as by being exposed to UV light at room temp.Optionally, a thin Si growth wafer background may be provided, such aswhere the Si growth wafer is approximately 100 μm or less, such as 75 μmor less, such as 50 μm or 40 μm or even 30 μm or less, and positioned ontop of the glass layer. In FIG. 29C, the 2D nanomaterial is releasedfrom the growth platform. In FIG. 29D, the 2D nanomaterial is bonded toa target wafer, and in FIG. 29E, the bond structure is exposed to alaser to release the glass. In FIG. 29F, a tape or other adhesivematerial-containing strip may be applied to provide an adhesive materiallayer. In FIG. 29G, this adhesive material layer may be peeled off andthe remaining structure may be cleaned.

The glass carrier used may be transparent to UV light, which allows bothfor curing of the adhesive material and to effectuate release, e.g., byan infrared laser, in the glass release step. As indicated, LTHC is auseful release layer. Particularly, the adhesive material may be filledwith Carbon black to absorb IR 1064 laser energy, may be heated to ahigh temperature, and thereby decomposed. In certain instances, LTHC maybe spun on in a thin layer. In particular examples, the adhesivematerial may be an acrylate, such as PMMA. More particularly, theadhesive material may be spun on so as to form an approximately 50 μmthick layer. Such adhesive materials are typically available in severaldifferent, e.g., four, different tacks, and where desired, othermaterials may be added to further reduce tackiness. An adhesive material5032 4% may be employed such as a low tack material.

For bonding, the surface to be bonded may be brought in close proximityto the adhesive material layer (<1 mm) in a vacuum. A top wafer may bedropped onto the adhesive material layer on the glass carrier viagravity. UV or other high intensity light or heat may be applied untilfully cured. The adhesive material may be such that it is resistant tosolvents, and can be exposed up to 220 C. The 2D nanomaterial may thenbe released, such as from a metal backing layer, e.g., composed ofcopper, silver, gold, or platinum, such as through a bubble bathmechanism or a mechanical peel process, as herein described. Thisprocess allows for continuous probing of the material layers to insurethe presence and/or uniformity of the 2D nanomaterial. After the carrierwith the 2D nanomaterial is placed on the target wafer, it may beadhesion baked, such as at 150 C for a short period of time, e.g., twominutes. The mechanism for the release from the glass may be to rasterthe structure with a UV laser for another short period of time, e.g.,two minutes. The tape may be applied by a manual vacuum chuck to holdthe wafer, and then a roller tape may be applied, e.g., manually.Alternatively dicing tape may be used. After peeling off the tape andthe adhesive layer, anneal cleaning is performed at 400 C.

FIGS. 30 and 31 illustrate an adhesive temporary bond material processusing a TZNR adhesive, e.g., from TOK (Tokyo Ohka Kogyo Co., Ltd.). Asshown in FIG. 30, the process involves adhesive spin coating of a growthsubstrate with a 1D or 2D layer, e.g., a graphene layer, so as todeposit the graphene layer onto the growth substrate. The compositionmay then be subjected to a curing step, such as by pre-baking, andaligned with a support wafer, where bonding may occur. For instance,thermal bonding may be effectuated by applying heat under a vacuum, suchas at a low bonding pressure (0.012 MPa). FIG. 31 illustrates the lowstress debonding by dissolving the adhesive, such as in addition tosolvent injection, pick up, and detachment such as by a handler. The 1Dor 2D containing substrate may then be cleaned so as to remove theresidue so that no residue is left on the device wafer.

FIGS. 32A-32E illustrate the adhesive temporary bond process with anickel (“Ni”) deposition layer. As shown in FIG. 32A, a metal such as Nimay be deposited on the 2D nanomaterial layer (in black). As shown inFIG. 32B, a tape lamination may be applied to the Ni layer. As shown inFIG. 32C, the tape layer may be peeled away from the growth platform andthe tape layer, Ni layer, and 2D nanomaterial layer may be transferredto a target wafer. Alternatively, the structure may be baked to improvethe 2D nanomaterial adhesion. As shown in FIG. 32D, the tape may bepeeled from the Ni layer (possibly with a release mechanism). As shownin FIG. 32E, a wet etch process may be used to remove the Ni layer.

ChemFET Manufacturing Process

In another aspect of the disclosure, various methods are provided. Forinstance, as described herein and above, a method for manufacturing aChemFET may be provided. The method may include depositing a channelnanomaterial, e.g., included of a one-dimensional (1D) ortwo-dimensional (2D) transistor nanomaterial, on an exposed metal layerportion of an integrated circuit structure, such as where the integratedcircuit structure includes a semiconductor substrate and/or a dielectriclayer. In such an instance, the metal layer may be configured so as toform a source and drain electrode, where the source and drain electrodesare separated from one another so as to form a channel region.

Accordingly, in certain instances, the metal layer(s) may be imbeddedwithin the dielectric layer and exposed so as to stand off therefrom.For instance, a patterned material may be used to expose a portion ofthe channel area and a plurality of adjacent areas. Particularly, thismay be performed such as by etching the dielectric material startingwith the adjacent areas thereby exposing a trench under the channel,and/or exposing the metal in the channel area. Additionally, the methodmay include etching the metal from underneath the channel to create aChemFET. In certain instances, a channel nanomaterial may be providedsuch as before, after, or during the etching process so as to form achannel between the exposed source and drain electrodes.

Additionally, a method for manufacturing a well formation for a 1D or 2Dnanomaterial FET may include depositing an organic passivation layerover a conductive channel of a 1D or 2D nanomaterial FET of asemiconductor device structure, patterning the organic passivation layerto create well formation locations over the channel, and removing thepassivation layer over the channel to expose the channel within the wellformation.

Further, in various examples, the method for manufacturing a wellformation for a 1D or 2D nanomaterial FET may include depositing apassivation layer over a conductive channel of a 1D or 2D transistormaterial FET of a semiconductor device structure, as described herein.Additionally, the method may include a first etching step for etchingthrough the majority of the passivation layer with a first etchingmethod so as to create a majority of a well formation, such as over thechannel. A second etching step may take place for the etching of theremaining passivation layer over the channel to expose the channelwithin the well formation. In some instances, the depositing of thepassivation layer may be over a functional layer that is itselfpositioned over the conductive channel of 1D or 2D nanomaterial.

Where one or multiple etching steps are provided, the first etchingmethod may be a plasma method or laser method, wherein the plasma methodoptionally is an RIE, HDP, ICP or ECR method. The first etching methodmay be performed through a mask material that is patterned to shieldparts of the passivation dielectric layer from the first etching methodwhile having openings that expose other parts of the passivationdielectric layer to the first etching method, wherein the mask materialoptionally is a photoresist or a hard mask material. Additionally, asecond etching method may be provided such as where the second etchingstep is a wet or gaseous etching method, optionally an electrochemicalor chemical etching method, wherein the chemical etching methodoptionally includes an acid, an aqueous acid solution, or a bufferedacid solution, and wherein the second etching method optionally etchesthe protective layer without substantially etching or affecting thechannel nanomaterial. In particular examples, the first and/or secondetching method(s) is(are) predominantly an anisotropic etching method.In such instances, the first etching method may be performed so as toetch through a controlled depth in the protective material layer whereinthe control is provided by a time of etching in conjunction with therate of etching or the control is provided by an end point detection.

When producing a well structure, the well may have any suitable shape orsize of configuration. For instance, in one example, the shape of thewell formation when viewed from the top is a round or polygon shape. Insuch an instance, the largest width of the well formation when viewedfrom the top may be about 0.1 μm to about 10 μm. Further, when forming awell, in various instances, an array of two or more well formations maybe formed. Hence, the ratio of the pitch of two well formations to thelargest width of the well formations when viewed from the top may begreater than 1 and less than 10. Accordingly, when an array of wellformations are formed, the variation of the largest widths of the wellformations when viewed from the top in an array may be designed to havewell formations with the same largest widths, which widths may be lessthan about 10%. In various instances, the well formation configurationmay be chosen with respect to consideration of fluid dynamics of a fluidflowing over or into the well formation, wherein consideration of fluiddynamics includes transport of reagents or particles over or into thewell formation.

In various instances, the method may include preparing a growthsubstrate of a 1D or 2D nanomaterial. In such an instance, the methodmay include depositing a metal catalyst layer on a substrate, optionallya wafer or a plate and annealing the metal catalyst. The 2D nanomaterialmay be a transistor material selected from the group including graphene,molybdenum disulfide (MoS2), phosphorene (black phosphorous), silicene,borophene, tungsten disulfide (WS2), boron nitride, WSe2, stanene (2Dtin), graphene, germanane, nickel HITP, Mxenes (Ti2C, (Ti0.5,Nb0.5),V2C, Nb2C, Ti3C2, Ti3CN, Nb4C3, Ta4C3), and a metal dichalcogenides.Further, the metal may be Cu, Ni, or Pt, or the like. Further still, aphotoresist may be included, such as where the patterned material is aphotoresist, which may be patterned using a photolithographic process.Likewise, the semiconductor substrate may be a Si material, a SiGematerial, or a material. Therefore, in accordance with these methods,the semiconductor device structure may be configured as or otherwisebased on CMOS, BiCMOS, Bipolar, or other fabrication technology; and theintegrated circuit may be configured as or based on FET, BJT, HBT, orother transistor technology.

Accordingly, the methods may include one or more of the followingetching steps, which may be executed in any logical order: etching thedielectric, where the etching includes: a plasma etching process,wherein the plasma etching process optionally includes an RIE, ICP, HDP,or ECR process; etching the dielectric, where the etching includes (i) awet or gaseous etching method, wherein the wet or gaseous etching methodoptionally is an electrochemical or chemical etching method, wherein thechemical etching method optionally includes an acid, an aqueous acidsolution, or a buffered acid solution; or (ii) an isotropic etchingmethod; and wherein the etching optionally etches the dielectric withoutsubstantially etching or affecting the channel nanomaterial; etching themetal, where the etching includes a plasma etching process, optionally(i) an RIE, ICP, HDP, or ECR process; (ii) a wet or gaseous etchingmethod, optionally an electrochemical or chemical etching method,wherein the chemical etching method optionally includes an acid, anaqueous acid solution, or a buffered acid solution; and (iii) whereinthe etching includes predominantly an isotropic etching method; etchingthe metal, where the etching is predominantly an isotropic etchingmethod; and etching the metal, where the etching etches the metalwithout substantially etching or affecting the channel nanomaterial.

As indicated, the dielectric layer may include a first thin layer ofmaterial forming an etch stop layer under the channel to limit theextent of the dielectric etching, wherein the first thin layer ofmaterial optionally includes a silicon oxide, a silicon nitride, or asilicon carbide or a non-stoichiometric material, and wherein the firstthin layer of material optionally is about 0.1 nm to 100 nm thick.Additionally, one or more functional layers may be deposited over thegraphene channel prior to etching the dielectric, wherein etching thedielectric may optionally include (i) a plasma etching process, whichplasma etching process optionally is an RIE, ICP, HDP, or ECR process;(ii) a wet or gaseous etching method, wherein the wet or gaseous etchingmethod is an electrochemical or chemical etching method, wherein thechemical etching method optionally includes an acid, an aqueous acidsolution, or a buffered acid solution; and (iii) wherein etching thedielectric optionally etches the dielectric without substantiallyetching or affecting the channel nanomaterial and without substantiallyetching or affecting the functional material. The one or more functionallayers may be deposited over the graphene channel subsequent to etchingthe dielectric.

Where a passivation layer is employed, the passivation layer may beincluded of an inorganic material, optionally an oxide, a nitride, acarbide, an oxy-nitride, a carbon-doped oxide, or a fluorine-doped oxidematerial. Additionally, the passivation layer may be included of anorganic material, optionally a polymer, polyimide, BCB, PBO or otherlike material. Further, the passivation layer may include multiplelayers of material. Hence, the passivation layer may be included of bothinorganic and organic materials. In certain instances, the passivationlayer may be deposited by a CVD, PECVD, PVD, ALD, or spin-on dielectricprocess. In various instances, the passivation layer may include a firstthin layer of material forming an etch stop layer over the channel and asecond thicker layer of passivation material over the etch stop layer,wherein optionally (i) the first etching method has high selectivity foretching the second thicker layer of passivation material as compared tothe first thin layer of material, (ii) the first thin layer of ESLmaterial is about 0.1 nm to about 100 nm thick and the second thickerlayer of material is about 0.1 μm to about 10 μm thick, (iii) the firstthin layer of material is included of a silicon nitride or a siliconcarbide, (iv) the first layer of thin material may be included of anon-stoichiometric material, and (v) the first etching method etchesthrough the second thicker layer of passivation material and stops onthe first thin layer of ESL material.

Simple Manufacturing Process Flow with Bottom Contacts

FIGS. 33A-33I provide exemplary diagrams of a semiconductor substrate atdifferent stages of treatment to create ChemFET for biosensing (e.g.,nucleic acid hybridization and/or sequencing) as described herein. Thismethod and resulting structure is characterized by the fact that theelectrodes contact the nanomaterial, e.g., graphene from underneath thegraphene layer (430) (i.e., the graphene is deposited on top of thesource and drain electrodes (422 and 424). At FIG. 33A, an insulateddielectric layer 420 is formed on a semiconductor substrate (410), e.g.,silicon or other semiconductors. Transistors and interconnects onsemiconductor substrate (410) may be present in some examples, but arenot depicted in FIGS. 33A-33I. A conductive material layer (428) maythen be formed over insulated dielectric layer (420, see FIG. 33B). Insome examples, the conductive material layer may be deposited intrenches formed in a dielectric layer (420).

The conductive material layer (428) may then be patterned to form asource electrode (422) and a drain electrode (424) (FIG. 33C). A 1D or2D nanomaterial layer (430) may then be applied over the electrodes(422, 424) and insulated dielectric layer (420, FIG. 33D). An analyte orion sensitive layer (434) may then be applied over the 1D or 2Dnanomaterial layer (430, see FIG. 33E). The ion sensitive layer (434)and 2D nanomaterial layer (430) may then be patterned (see FIG. 33F fora side sectional view and see FIG. 33G for a top-down view) usingtechniques described herein. In certain examples, holes or openings maybe created in ion sensitive layer (434) and 2D nanomaterial layer (430),as described above, and a second conductive layer may be placed on topof the openings or holes to electrically contact the electrodes (422,424). A passivation layer (435) may then be added on top of electrodes(422, 424) as well as the ion sensitive layer (434) and 2D nanomateriallayer (430, see FIG. 33H) and then patterned to form a chamber (437, seeFIG. 33I)

CMOS Integration with Top Down Graphene Contacts

FIGS. 34A-34J are side sectional views that illustrate a preferred CMOSintegration method for building the interconnects, dielectric and wellstructures, as well as the pads for bonding the chip to a package, 1D or2D nanomaterial transfer to the chip and 1D or 2D material patterning.For instance, FIG. 34A illustrates a graphene material layer (430)deposited or formed on a ROIC semiconductor wafer, such as a CMOS wafer,that includes a semiconductor substrate (410), a dielectric layer overthe substrate (420) and one or metal layers in or on the dielectriclayer that form interconnects, including a conductive source (422) anddrain (424). FIG. 34B illustrates patterning the graphene layer (430) toform a channel, which extends horizontally from the source to the drain.FIG. 34C illustrates an etch stop layer (ESL) (474) deposited over thegraphene layer (430). FIG. 34D illustrates a deposited, patterned, andetched thick insulator layer (435) over the ESL (474), with the etchedfeatures stopping on the ESL layer (474). FIG. 34E illustrates an etchedESL (474), either dry or wet etched, and further etching of theunderlying dielectric layer (420), such as by a plasma etch such as aRIE, stopping on a metal interconnect layer, i.e., the source (422) anddrain (424). FIG. 34F illustrates the filling of the etched trenches,such as by a damascene copper process comprising depositing a barrier,depositing a liner, copper electroplating and Chemical MechanicalPolishing (CMP). There may be an optional addition of a work functionmatching material prior to the damascene trench fill process.

FIG. 34G illustrates a deposit of a barrier/adhesion layer, deposit of abondable pad material and an interconnect material, such as aluminum,patterning and etching of the aluminum interconnect and the pad layer.FIG. 34H illustrates a deposit of SiO2 (435) (e.g., CVD), CMP, and a padopen etch to expose the bond pad (448). FIG. 34I illustrates a DRIE ofthe passivation insulator (435) down to the etch stop layer (474),forming a majority of a well structure (438). FIG. 34J illustrates a wetetch of the thin etch stop layer (474) to expose the channel (430)within the chamber (437) of the well structure (438). In a case wherethere is an analyte or reaction-sensitive layer (not shown) over thechannel material there may be a possibility to use a dry etch process toremove the remaining thin etch stop layer (474), in which case the dryetching would stop on the analyte or reaction-sensitive layer. Thus, asillustrated in FIGS. 34A-L a ChemFET is formed which includes metalcontacts to the channel (430) from above the channel rather than frombelow the channel as in FIGS. 33A-I.

Improved fabrication techniques employing 1D, 2D (e.g., graphene), or 3Dnanomaterials as a channel layer or sensing layer or structure providefor rapid data acquisition from small sensors to large and dense arraysof sensors. Such arrays may be employed to detect the presence and/orconcentration changes of various analyte types in a wide variety ofchemical and/or biological processes, including DNA or RNAhybridization, and/or nucleotide and/or protein sequencing and/ordetection reactions.

Accordingly, in particularly examples, chemically-sensitive graphenefield effect transistor (gFET) arrays (as well as arrays made from otherchemically-sensitive 1D or 2D nanomaterials) facilitate genetic and/orprotein sequencing and/or detection techniques based on monitoringchanges in various reactants within a zone associated with the array,such as changes in ion concentration, e.g., changes in hydrogen (pH) orother ion concentration, or changes in other analyte concentrations,and/or binding events associated with chemical or biological processessuch as nucleic acid synthesis (as used in NGS and other nucleic acidsequencing approaches), or biologic activity such as within a reactionwell or chamber of the gFET based sensor, e.g., a gated sensinglocation.

Particularly, the present disclosure concerns chemically-sensitive 1D or2D nanomaterial layered FETs for analysis of biological and/or chemicalanalytes or reactions or biologic activity. Such ChemFETs solve many ofthe current problems associated with nucleic acid detection, sequencing,genetic, and/or molecular diagnostics.

Accordingly, provided herein are systems for analysis of biologicaland/or chemical materials or analytes, chemical reactions, or biologicactivity. In various examples, the system includes a ChemFET, such ashaving a substrate that includes one or more wells or chamber and/orchannel arrangements therein, such as where the well, chamber and/orchannel thereof may be associated with one or more sensors. Inparticular instances, a solution-gated ChemFET with an associated wellor chamber structure is provided, such as where the well and/or chamberstructure is configured such that a biological and/or chemical reactioncan take place within the well or chamber, such as proximate a ChemFETchannel structure therein that is included of a chemically sensitive 1Dor 2D transistor nanomaterial. In various instances, the well or chamberis positioned on a portion of the substrate so as to align with anexterior surface of the channel of each sensor, wherein the channel is aconductive channel that extends from the conductive source to theconductive drain of the ChemFET. The well and/or chamber structuretypically defines an opening that allows for direct fluid contact withthe channel or an associated member thereof. The well or chamberstructure may be made of an insulator passivation material, such as aninorganic material such as silicon oxide or silicon nitride.Alternatively, the insulator material for the well or chamber structurecan be an organic material such as a polyimide, BCB, PBO or other likematerials.

In various instances, the length of the interior surface, e.g., thechannel, of the ChemFET, such as from the source to the drain, rangesfrom about 0.05 micron to about 3 microns, and a width of the surfaceand/or channel may range from about 0.5 micron to about 2 microns. Inparticular instances, the well or chamber structure can be configured toinclude or otherwise be associated with a nucleic acid template orprobe, such as a nucleic acid that may be directly or indirectlyimmobilized (covalently or non-covalently) on a surface of the well orchamber.

For instance, in certain instances, the nucleic acid template (in thecontext of sequencing reactions) or probe (in the context ofhybridization reactions) can be bound to or otherwise immobilized on aninterior surface of the well or chamber, such as on the substrateitself, or a layer associated therewith, e.g., a layer composed of a 1Dor 2D transistor nanomaterial or a material coating or covering the 1Dor 2D transistor nanomaterial, such as a sensing layer and/orpassivation layer.

In other examples, the nucleic acid template or probe can be bound to asecondary substrate, such as a microbead or other particle positionedwithin the well or chamber so as to be proximate with thechemically-sensitive 1D, e.g., CNT or semiconductor NW, or 2D transistornanomaterial, e.g., graphene. Additional alternative 2D nanomaterialsfor the channel may include silicene, molybdenum disulfide, blackphosphorous (phosphorene), borophene, tungsten disulfide, boron nitride,tungsten diselenide, stanene, germanane, nickel HITP, and/or metaldichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C,

Attachment of Capture Agents, Arrangement of Microbeads and SensingModality

FIG. 20A is an illustration of electrowetting for biomoleculeattachment, as described herein. In certain examples, attachment (alsoreferred to as functionalization) of biomolecules such as capture agentsto the graphene channel of the individual gFETs is performed byelectrically controlling movement of one or more droplets containing thecapture agents. As depicted in the top diagram a droplet may bedispensed on a surface of the chip near an electrode. The droplet maycontain capture agents such as complementary DNA, antibodies, and othercapture agents. In the center diagram, one or more droplets containingthe capture agents are moved between electrodes by the application of avoltage to the new electrode, i.e., the electrode which was the dropletis to be attracted. In some examples of the voltage may be large such asfor example 100 V. The action of moving the one or more droplets leavesa trail of biomolecules on the surface of the chip. As illustrated, inthe bottom diagram of FIG. 20A, the one or more droplets can be moved inby applying voltages to electrodes such that the one or more dropletsremoved and the capture agents are left noncovalently attached to thegraphene channel, e.g., by noncovalent binding that occurs between thecapture agents and the top surface of the graphene.

FIG. 20B is an illustration of electrophoresis for biomoleculeattachment. As illustrated in the top diagram of FIG. 20B, a first stepin this type of functionalization includes positioning a dropletcontaining complementary DNA or other capture agents over a graphenechannel the individual gFETs. Next, as depicted in the middle diagram alarge voltage is applied to one of the electrodes connected to thegraphene channel such that the electrical potential drives thebiomolecules to be attached towards the graphene channel. With thecapture agents noncovalently bound to the graphene surface, the one ormore droplets can be washed off the region capture agents behind.

FIG. 20C is an illustration of microfluidics for biomolecule attachment.In this example, a microfluidic channel is positioned over the so as toflow over the graphene electrical channel. The microfluidic channel canbe permanent or temporary. For example, a permanent microfluidic channelmay be created as part of the chip. As the channel is created, a portionof the graphene is exposed such that contact is enabled between a topsurface of the graphene channel and capture agents in a liquid flowingthrough the microfluidic channel. As the liquid containing the captureagents flows over the graphene channel, capture agents in the liquid areenabled to bind to the graphene channel.

FIG. 20D is an illustration of an optical readout of DNA sequencingusing nanomaterials. More particularly, in such a configuration asrepresented in the figures, the drain current of the ChemFET (1) can bemodulated by the electrical charge carried by the nucleotide moleculesinvolved in the hybridization and/or sequencing reactions. For example,in one particular configuration of the FET, after hybridization or anelongation step, the charge in the sensing zone increases resulting in achange in the output current that may be measured. This measurement,e.g., for this configuration of the FET, may be made in accordance withthe following equation:

V _(THF) =V _(TH0)−(Q _(com) +Q ₀)/(CC+CF)

Such as where CC represents the current at the control capacitor, and CFrepresents the current at the parasitic capacitor. V_(THF) representsthe effective threshold voltage of the ChemFET (1), and V_(TH0)represents the native threshold voltage. Q₀ represents the electriccharge initially trapped in the floating gate, and Q_(com) (alsoreferred to as Q_(DNA)) represents the total charge of hybridizationcomplex.

For instance, a nucleic acid from a sample to be sequenced orrepresentative of a probe to be targeted may be immobilized on thebottom surface (21) or the sidewall (39) of the sample solution wellchamber (37). A DNA polymerase (e.g., an isothermal DNA polymerase,e.g., a Bst or Bst-like DNA polymerase), a nucleotide substrate, andother necessary reagents may then be introduced to the sample solutionchamber to induce an elongation reaction. As a result, DNAs may besynthesized using the immobilized nucleic acid as the template for DNAsynthesis. In such an instance, as the source-drain current vs. gatevoltage characteristic changes by the electrostatic interaction with thecharged particles (electrons, ions, etc.) in the well, the base sequenceof a template nucleic acid having a large base length can be sequencedand/or analyzed. In other examples, a nucleic acid probe may beimmobilized on the surface of the sensing zone, as described above, andused in a hybridization reaction so as to detect, for example, geneticvariation, the presence of a genetic disease, polymorphism, or pathogen.

In various instances, in order to conduct parallel analysis of aplurality of nucleic acid templates, the number of the ChemFETs may beequal to or higher than the number and/or types of DNAs to be sequencedand/or analyzed. In certain instances, each nucleic acid template orprobe may be an oligonucleotide or a fragment of DNA or RNA that may beconstituted from about 100 to about 1000 bases, such as from 200 toabout 800 bases, for instance, from about 300 or about 500 bases toabout 600 or 700 bases or more or somewhere in between. However, invarious instances, a fragment of nucleic acid having 100 bases or fewermay also be used.

Additionally, as indicated above, the present ChemFET device (1) mayalso be used in various different DNA/RNA hybridization reactions, suchas for the purpose of determining a genetic variation and/or fordetecting the presence of a genetic marker for a disease or pathogen. Insuch an instance, a nucleic acid probe may be coupled to or immobilizedon a bottom or side graphene-coated surface of the sensing chamber, perabove. As indicated, the probe may be of any suitable length but invarious instances from about 5 or 10 to about 1000 bases, such as from20 or about 50 to about 700 or about 800 bases, for instance, from about100 or about 200 bases to about 300 bases including about 400 or about500 bases to about 600 or 700 bases or more or somewhere in between.

For instance, in one exemplary example, a nucleic acid probe or templatecontaining about 20 to 50-100 bases coding for a gene sequence ofinterest that has been previously amplified or otherwise synthesized(e.g., by solid state synthesis methods), may be immobilized in orproximate to the channel region (30), a channel insulating film, and/ora side surface of the sensing chamber (37) of the ChemFET (1). Forexample, once isolated and amplified, the base of the probe may bemodified so as to be attached to the graphene coated surface, and/or maybe coupled to a secondary substrate, such as a polymer or plasticmicrobead (60) that has been chemically treated so as to be coupledtherewith.

Once immobilized, the sensing chamber (37) containing the probes, eitheron a secondary substrate or directly coupled with a chamber surface, maybe reacted with a sample solution containing a number genes including atarget gene of interest to be measured such that when a nucleic acidprobe having a complementary base sequence to the target gene isimmobilized on the channel (30), channel insulating film (34), or thesidewall surface (39) of the sample solution well structure (38), or ona secondary substrate immobilized within the sensing chamber of theChemFET device (1) for gene detection, the target gene hybridizes withthe nucleic acid probe under appropriate reaction conditions and thetarget gene and the nucleic acid probe form a double strand, the resultof which hybridization reaction may be detected.

ChemFET and ChemFET Sensor Array IC Chip Review

As depicted in FIG. 15F, a ChemFET sensor array IC chip (50) may bearranged as a two-dimensional ChemFET sensor array on an IC chip (50)that in this instance is based on a column and row design, althoughother designs are also possible. As can be seen with respect to FIG.15F, the system further includes a row and column decoder (144), as wellas circuitry for performing the requisite sensing, detecting, andprocessing so as to measure the sensory data. Hence, also included issensing, measurement, and other associated readout data.

Accordingly, as can be seen with respect to FIGS. 14A, 15A and 15B, invarious instances, a one or two-dimensional ChemFET array, as describedherein, may be fabricated on a ChemFET sensor IC chip (50) in accordancewith the methods herein disclosed. In various instances, the sensorarray chip may include a number of ChemFET sensors (1) that may bearranged in columns and/or rows. A typical number of sensors may includeChemFET sensor elements (1), described herein as “sensors,” that may bearranged in a 16 sensor by 16 sensor column/row array configuration. Asdepicted, the array includes two columns, but typically may includesixteen columns, arranged side by side, where each column includes 16rows. Particularly, each column of the array includes up to 16 sensors.Each column may be configured so as to include a current source Is thatmay be shared by all sensors of the column.

However, in various other examples, each sensor may have its own currentsource, or the array itself may have a single current source.Additionally, each ChemFET sensor (1) may include a ChemFET (1), asdescribed above, having an electrically coupled source and/or drainand/or body, and may further include one or more switches, such as aplurality of switches S1 and S2 that may be configured so as to beresponsive to one of the up to sixteen row select signals (RSEL, and itscomplements). More particularly, a row select signal and its complementmay be generated simultaneously to “enable” or select a given sensor ofthe selected column, and such signal pairs may be generated in somesequence to successively enable different sensors of the column, e.g.,together or one at a time, such as sequentially.

A row decoder (144) may also be provided as part of the system. In suchan instance, the row decoder may be configured so as to provide up tosixteen pairs of complementary row select signals, wherein each pair ofrow select signals may be adapted so as to simultaneously orsequentially enable one sensor in each column so as to provide a set ofcolumn output signals from the array, e.g., based on the respectivesource voltages V_(Sa) through V_(Sb), etc. of the enabled row ofChemFETs. The row decoder (144) may be implemented as a conventionalfour-to-sixteen decoder (e.g., a four-bit binary input ROW1-ROW4 toselect one of (24) outputs). The set of column output signals V_(Sa)through V_(Sb) for an enabled row of the array is applied to switchinglogic, which may be configured to include up to sixteen transmissiongates Sa through Sb (e.g., one transmission gate for each outputsignal).

As above, each transmission gate of the switching logic may beimplemented using an n-channel or p-channel MOSFET, such as wherevarious analog and/or digital transistors and circuits may be included,such as proximate the ChemFET sensor array. The transmission gate may bepositioned in a bottom or top gate configuration, or both to ensure asufficient dynamic range for each of the output signals V_(Sa) throughV_(Sb). The column decoder (144), like the row decoder (144), may beimplemented as a conventional four-to-sixteen bit decoder and may becontrolled via the four-bit binary input COL1-COL4 to enable one of thetransmission gates Sa through Sb of the switching logic at any giventime, so as to provide a single output signal VS from the switchinglogic. This output signal VS may be applied to a 10-bit analog todigital converter (ADC) (141) to provide a digital representation D1-D10of the output signal VS corresponding to a given sensor of the array.

As noted earlier, individual ChemFETs and arrays of ChemFETs such asthose discussed above may be employed as sensing devices in a variety ofapplications involving chemistry and biology. In particular, suchChemFETs may be employed as pH sensors in various processes involvingnucleic acids such as DNA. In general, the development of rapid andsensitive nucleic acid hybridization and sequencing methods, as hereindescribed, e.g., utilizing automated DNA sequencers, may significantlyadvance the understanding of biology.

It should be noted, that with respect to the various arrays disclosedherein according to various examples of the present disclosure may befabricated according to conventional CMOS fabrication techniques, asdescribed above, as well as modified CMOS fabrication techniques (e.g.,to facilitate realization of various functional aspects of the ChemFETsensor array IC chip (50) discussed herein, such as additionaldeposition of graphene and/or other passivation materials, process stepsto mitigate trapped charge, etc.) and other semiconductor fabricationtechniques beyond those conventionally employed in typical CMOSfabrication (e.g., BiCMOS).

Additionally, various lithography techniques may be employed as part ofan array fabrication process. For example, in one exemplaryimplementation, a lithography technique may be employed in whichappropriately designed blocks are “stitched” together by overlapping theedges of a step and repeat lithography exposures on a wafer substrate byapproximately 0.2 micrometers. In a single exposure, the maximum diesize typically is approximately (21) millimeters by (21) millimeters. Byselectively exposing different blocks (sides, top & bottoms, core, etc.)very large chips can be defined on a wafer (up to a maximum, in theextreme, of one chip per wafer, commonly referred to as “wafer scaleintegration”).

In one example, the array includes 512 columns with corresponding columnbias/readout circuitry (one for each column), wherein each columnincludes geometrically square sensors, each having a size ofapproximately 9 micrometers by 9 micrometers (e.g., the array may be upto 512 columns by 512 rows). In various instances, the entire array(including sensors together with associated row and column selectcircuitry and column bias/readout circuitry) may be fabricated on asemiconductor die as an application specific integrated circuit (ASIC),structured ASIC, or as a field gated programmable array such as havingdimensions of approximately 7 millimeters by 7 millimeters.

Various power supply and bias voltages useful for array operation areprovided to the array via electrical connections (e.g., pins, metalpads) and labeled for simplicity in block as “supply and biasconnections.” The array may also include a row select shift register,one or more, e.g., two sets of column select shift registers, and one ormore, e.g., two, output drivers, which output drivers are configured toprovide two parallel output signals from the array, V_(outa) andV_(outb), representing sensor measurements. The various power supply andbias voltages, control signals for the row and column shift registers,and control signals for the column bias/readout circuitry may beprovided by an array controller, which controller may also read theoutput signals V_(outa) and V_(outb) (and other optionalstatus/diagnostic signals) from the array. Configuring the array suchthat multiple regions (e.g., multiple columns) of the array may be readat the same time via multiple parallel array outputs (e.g., V_(outa) andV_(outb)) facilitates increased data acquisition rates.

Accordingly, in various examples, a ChemFET sensor IC chip (50) in forperforming a sequencing reaction is provided, such as where thesequencing reaction involves the sequencing of strands of nucleic acids,as described herein. In various examples, the ChemFET sensor IC chip(50) may include a substrate and an array of graphene ChemFETs (1)arranged on the substrate. In such an example, one or more of, e.g.,each, of the graphene field effect transistors may include a primarylayer forming a base layer (10), and a secondary, e.g., intermediary,layer positioned over or otherwise associated with the primary layer,the secondary layer (20) being formed of a first nonconductive materialand including a source (22) and a drain (24) formed in the firstnonconductive material (20), the source (22) and drain (24) beingseparated one from the other by a channel (30), and being formed of anelectrically conductive material.

In certain instances, a tertiary layer (35) may be positioned over thesecondary layer, such as where the tertiary layer includes a solutiongate formed over the channel (30) to electrically connect the source andthe drain. In such an instance, the channel (30) may be formed of agraphene layer. The tertiary layer (35) may additionally include asurface structure that overlaps the source and the drain in thesecondary layer (20), the surface structure further defining a well (38)having side walls (39) and a bottom (21) that extends over at least aportion of the graphene layer of the channel so as to form a sensingchamber (37) for the performance of the sequencing reaction. Inparticular examples, a nano- or microbead (60) provided in one or morewells (38) of the array of graphene field effect transistors, such aswhere one or more, e.g., each microbead (60) may be configured with oneor more reactants to interact with portions of the strands of nucleicacids such that the associated chemically sensitive FET detects a changein ion concentration of the reactants by a change in current flow fromthe source to the drain via an activation of the graphene layer.

It should be noted that, in various examples of the ChemFET sensor ICchip (50), one or more of the columns, e.g., the first and last columns,as well as the first and/or last ChemFET sensors (1) of each of thecolumns may be configured as “reference” or “dummy” ChemFET sensors (1).For instance, the dummy sensors of an array, e.g., the topmost metallayer of each dummy sensor may be tied to the same metal layer of otherdummy sensors and may be made accessible as a terminal of the chip,which in turn may be coupled to a reference voltage VREF. Such referencevoltage VREF may be applied to the bias/readout circuitry of respectivecolumns of the array.

In some exemplary implementations, preliminary test/evaluation data maybe acquired from the array based on applying the reference voltage VREFand selecting and reading out dummy sensors, and/or reading out columnsbased on the direct application of VREF to respective column buffers(e.g., via the CAL signal), to facilitate offset determination (e.g.,sensor-to-sensor and column-to-column variances) and array calibration.The calibration data can be stored for each sensor location either justprior to a sequencing session, or at the end of the device manufacturingprocess. The calibration data can be stored on-chip, such as innon-volatile memory.

Additionally, in a further aspect of the present disclosure, a ChemFET(1) having a chamber (37) and/or channel (30) including a 1D or 2Dnanomaterial and/or 3D material may be provided, such as where the 1D or2D nanomaterial and/or 3D material is present within and/or proximatethe chamber (37) and/or channel (30) and configured in such a manner sothat the chamber (37) and/or channel (30) geometry may be optimized soas to maximize the ratio of channel width (W) to channel length (L).

In various instances, this can be done through the use of interdigitatedsource and drain electrode geometries, such as in a single plane or, inother examples, such optimization may be achieved through the use of oneor more 3D electrode structures, such as configured to at leastpartially or fully circumscribe the chamber (37) or well (38). Forinstance, as can be seen with respect to FIG. 5G, various source (22)and/or drain (24) electrodes may be configured as planar structures thatare adapted so as to interact with one another in such a manner to moreaccurately detect the presence of a chemical reaction, e.g., thepresence of a biomolecule, that occurs proximate the source (22) anddrain (24) electrodes.

In various instances, the source (22) and drain electrodes (24), as setforth in FIG. 5G may be formed in such a manner so as to have aninterdigitated configuration, such as where one or more of theelectrodes, or a portion thereof, are adapted so as to be fit one withinthe other, such as where one electrode portion is configured as animpingement member, and the other is configured as a receiving member.In particular examples, the source (22) and drain (24) electrodes areconfigured so as to include pronged, fork-like appendages that arecapable of being fitted one within the cavity of the other, such asbetween adjacent prong members.

For example, as seen with respect to FIG. 5G, the source and drainelectrodes may form electrode pairs, such as where one or more of thesource (22) and drain (24) electrodes may have a planar and/or extendedand/or interdigitated design, such as where one, e.g., the first, of theelectrode pair forms one or more cavities and the other, e.g., thesecond, of the electrode pair forms an impingement member for insertionwithin the one or more of the cavities of the first electrode.Particularly, in various implementations, one or more of the electrodepairs may have a linear configuration, while the second of the pair mayhave a linear, curved, or curvilinear configuration. In particularexamples, both the source (22) and drain (24) electrodes may both becurvilinear or curved.

More particularly, as can be seen with respect to FIG. 12, a FET sensor(1) having a well structure (38) is provided. Particularly, FIG. 12depicts a cross-section of a well opening stopping on an analyte orreaction-sensitive layer (34). For instance, FIG. 12 provides asubstrate, such as silicon and/or silicon dioxide substrate (10/20),where the substrate is configured so as to include a chamber, such as achamber having a formed well (38) that may be positioned over an analyteor reaction-sensitive layer (34) that may be positioned on top of thatsubstrate (10) and/or an associated oxide layer (20). For instance, inaccordance with the methods disclosed herein, such a well (38) may beformed by any suitable method such as by a dry etching process, such asby a plasma or RIE process. In particular instances, the etching processmay be selective to the well material so that the well etch can bestopped on the analyte or reaction-sensitive layer (34) withoutsignificant damage or etching of the analyte or reaction-sensitive layer(34).

Accordingly, in one aspect of the present disclosure a method forforming a semiconductor wafer is provided, wherein the wafer isconfigured as transistor on which a 1D or 2D nanomaterial layer may bepositioned. The method may include providing a wafer, such as a waferconfigured as or to otherwise include an integrated circuit, so as toform a semiconductor wafer. The wafer may include a substrate, such as asilicon substrate. An insulating layer may be applied to the substrate,such as via CVD of a silicon dioxide layer. A 1D or 2D nanomaterial maythen be applied, hence, the method may include patterning the 1D or 2Dnanomaterial layer so as to define 1D or 2D nanomaterial channels orchambers or wells, where such channels may be aligned with interconnectlines on the semiconductor wafer.

In various instances, the method may also include depositing a firstdielectric layer over the channels, chambers, or wells. The method mayalso include opening holes or trenches in the first dielectric layerwherein some of the holes may be aligned to the channels, chambers, orwells, and some of which may be aligned to the interconnect lines. Themethod may also include depositing conductive material on the 1D or 2Dnanomaterial layer, such as in the holes or trenches so as to createvias that contact the interconnect lines and/or the channels, chambers,or wells. Additionally, the method may include depositing and patterninga set of second interconnect lines over the dielectric layer andcontacting the vias. In some examples, the method may include depositinga second dielectric layer over the first dielectric layer and the secondinterconnect lines. Particularly, the method may also include patterningand opening holes or trenches in the second dielectric layer to exposeportions of the second interconnect lines to be used as pads. The methodmay also include patterning and opening holes or trenches in the secondand first dielectric layers to expose portions of the channels.

Hence, in particular examples, a method for forming a semiconductorwafer with transistors on which a 1D or 2D nanomaterial layer may bedeposited is provided. The method may include providing a semiconductorwafer having a substrate and/or insulating layer upon which a 1D and or2D nanomaterial layer is deposited. The method may then includepatterning the 1D or 2D nanomaterial layer to define 1D or 2Dnanomaterial channels, chambers, or wells, where the channels, chambers,or wells may be aligned with interconnect lines on the semiconductorwafer. The method may also include depositing an etch stop layer over orwithin the channels, chambers, or wells. The method may also includedepositing a first dielectric layer over the etch stop layer, openingholes or trenches in the first dielectric layer, such as where some ofthe holes or trenches are aligned to the channels, wells, and/orchambers, and some of which are aligned to the interconnect lines.

The method may also include depositing conductive material in the holesor trenches to create vias that contact the interconnect lines and thechannels. In such an instance, the method may include depositing andpatterning a set of second interconnect lines over the dielectric layerand contacting the vias. The method also includes depositing a seconddielectric layer over the first dielectric layer and the secondinterconnect lines. The method may include patterning and opening holesor trenches in the second dielectric layer to expose portions of thesecond interconnect lines to be used as pads. The method mayadditionally include patterning and opening holes or trenches in thesecond and first dielectric layers to expose the etch stop layer overthe channels.

The method also includes opening holes or trenches in the etch stoplayer to expose portions of the channels, chambers, or wells.

Particularly, another aspect of the present disclosure is a method forforming a semiconductor wafer with transistors on which is a 2Dnanomaterial layer. The method may include patterning the 2Dnanomaterial layer to define 2D nanomaterial channels, chambers, orwells, said channels, chambers, or wells being aligned with interconnectlines on the semiconductor wafer. The method also includes depositing anetch stop layer over the channels and/or depositing a first dielectriclayer over the etch stop layer. Holes or trenches may be opened in thefirst dielectric layer and aligned to the channels, chambers, or wellsand/or aligned to the interconnect lines. Conductive material may bedeposited in the holes or trenches so as to create vias that may beconfigured to contact the interconnect lines and the channels, chambers,and/or wells.

A set of second interconnect lines may be deposited and patterned overthe dielectric layer so as to contact the vias. A second dielectriclayer may also be deposited over the first dielectric layer and/or thesecond interconnect lines, and holes or trenches may be patterned toprovide openings in the second dielectric layer so as to expose portionsof the second interconnect lines, which may be used as pads. In such aninstance, the method may also include patterning and opening holes ortrenches in the second and first dielectric layers using an anisotropicetching process to expose the etch stop layer over the channels, wells,or chambers. The method may also include opening holes or trenches inthe etch stop layer to expose portions of the channels, chambers, orwells.

In certain instances, a method for forming a semiconductor wafer havingone or more transistors on which a 1D or 2D nanomaterial layer may bedeposited, as herein described. The method may include patterning the 1Dor 2D nanomaterial layer to define 2D nanomaterial channels, saidchannels being aligned with interconnect lines on the semiconductorwafer. The method may also include depositing an etch stop layer overthe channels. The method includes depositing a first dielectric layerover the etch stop layer and/or opening holes or trenches in the firstdielectric layer, where some of which may be aligned to the channels andsome of which may be aligned to the interconnect lines.

In various instances, the method also includes depositing conductivematerial in the holes or trenches to create vias that contact theinterconnect lines and the channels. In such an instance, the method mayinclude depositing and patterning a set of second interconnect linesover the dielectric layer and contacting the vias. In certain instances,a second dielectric layer may be deposited over the first dielectriclayer and the second interconnect lines. In such an instance, the methodmay include patterning and opening holes or trenches in the seconddielectric layer to expose portions of the second interconnect linesthat may be used as pads. The method may include patterning and openingholes or trenches in the second and first dielectric layers, such as byusing an anisotropic etching process to expose the etch stop layer overthe channels.

Accordingly, in particular instances, the semiconductor structure mayinclude a plurality of 1D or 2D nanomaterial channels, chambers, orwells composed of a 1D or 2D nanomaterial, an etch stop layer, aplurality interconnect lines on a semiconductor wafer, a firstdielectric layer comprising a plurality of holes or trenches, aconductive material, a second plurality of interconnect lines, and asecond dielectric layer having a plurality of holes or trenches. And insome examples, the semiconductor structure includes a plurality of 1D or2D nanomaterial channels, chambers, or wells composed of a 1D or 2Dnanomaterial, a plurality interconnect lines on a semiconductor wafer, afirst dielectric layer comprising a plurality of holes or trenches, aconductive material, a second plurality of interconnect lines, and asecond dielectric layer having a plurality of holes or trenches.

Further, in various instances, the ChemFET (1) may optionally includeone or more of an ion-selective permeable membrane (40), a charge trapscreening layer (42), such as hexagonal boron nitride (hBN) or HMDS, anion getter (41) such as phosphorous-silicate glass (PSG) and/or areference electrode (66). For instance, an ion-selective membrane (40)may be included, such as where the membrane preferentially allows ionsof interest (68) to pass through the membrane (40), so as to interactwith the channel (30), as compared to ions not of interest (69).Likewise, a charge trap screening material (42), e.g., an HMDS or hBN,may be included and configured to manage the interaction of the channel(30) with an underlying oxide layer (20). In similar fashion, an iongetter (41), such as PSG, may be deposited on or near the channel (30),such as on the chamber (37) sidewalls (39) in order to trap or sequesterions that would interfere with the detection and analysis of ions ofinterest interacting with the ChemFET (1).

In various examples, the ChemFET (1) may be configured to include agate, such as a solution gate, and may include a reference electrode(66) applying a gate voltage to the solution. In some examples, a backgate region may also be included. Such a back gate can be implementedeither as a global back gate (80), i.e., the same backgate voltage isapplied to the semiconductor substrate (10) of the ChemFET (1), or as alocal backgate (82), wherein there are a plurality of backgateelectrodes (82), e.g., one backgate electrode (82) is individuallyassociated with each ChemFET (1) channel (30), the backgate electrode(82) formed in an interconnect layer of the ChemFET (1) and used toapply a local backgate voltage to the channel (30) to which it isassociated. Furthermore, by applying both a solution gate and a backgatein concert, i.e., as a dual gate, the sensitivity of the ChemFET can beextended past the Nernst limit of 59 mV/pH.

In particular instances, the conductive source and the conductive drainof the ChemFET may include a metal material, such as a copper material,e.g., a damascene copper, an aluminum material, a platinum material, agold material, and the like. For instance, the conductive source and theconductive drain may be embedded in a dielectric and/or an insulatormaterial, such as an oxide layer, which oxide layer may be positionedover a substrate layer. In particular examples, the source and drain maybe configured so as to be planar with a top surface of the insulator,and in other examples, as described herein above, may be configured soas to extend above the insulator material layer in which they areembedded.

Analyte or Reaction-Sensitive Layer

In certain instances, a further insulating layer, e.g., an oxide layer,may be included and positioned above the first dielectric layer and/orthe channel nanomaterial layer. Particularly, the channel nanomaterialmay be at least partially covered in a layer that is included of ananalyte or reaction-sensitive material, such as an ion sensitive oxidematerial, e.g., a material having a high intrinsic buffer capacity,which may have a thickness of 50 nanometers or less. In one example, thesecond oxide layer may itself include two or more oxide layers, whereinthe oxide layers may be included of an aluminum oxide, a silicondioxide, a hafnium dioxide, hafnium silicate, zirconium silicate,zirconium dioxide, lanthanum oxide, titanium oxide, tantalum oxide, ironoxide, or yttrium oxide.

Passivation and Well Structure

As described herein, in various examples, the ChemFET may include a wellstructure or chamber that is positioned on a portion of an exteriorsurface of the passivation, e.g., oxide, layer and may be positionedover the channel region and/or channel nanomaterial. For instance, thewell structure may be configured so as to define an opening allowing fordirect contact with the channel and/or analyte or reaction-sensitivelayers, and In some instances, the well structure may itself be composedof an insulator material. For example, the passivation material of thewell structure may be composed of an inorganic or organic material, suchas where the inorganic material may be a silicon oxide, a siliconnitride, a silicon oxynitride, a silicon carbide or other metal oxide,carbide or nitride, and the organic material may be a polymer,polyimide, BCB, PBO or other like material.

The ChemFET, e.g., a well or chamber thereof, may be configured forchemical or biological material detection, chemical reaction detectionor biologic activity detection, such as where the biological materialmay include one or more biological polymers, nucleic acids, such as DNAor RNA, proteins, carbohydrates, lipids, cells, virus particles,antibodies, peptides, polysaccharides, ions associated withbiomolecules, and the like.

In another aspect, a biosensor may be provided. In such an instance, thebiosensor may include at least one ChemFET that includes a wellstructure, as described above, where the well structure is positionedover a portion of an exterior surface of an insulation layer, e.g., adielectric or oxide layer, of the ChemFET(s). In certain instances, thewell structure defines an opening that is configured for receivingand/or retaining reactants thereby allowing for various interactions ofcompounds produced in a chemical reaction within the well to occur.Accordingly, in various instances, the well may be configured as asolution well and/or may include an electrode, such as a referenceelectrode, and/or may otherwise be configured as a solution gate. Inparticular instances, the well structure may be bounded by the firstdielectric or oxide layer, or may be bounded by the channel nanomateriallayer, and/or a secondary oxide layer.

Detecting an Analyte or Reaction Through a Shift in an I-V Curve

In particular examples, the biosensor may include a processor, such asproximate the substrate, which processor may be in electricalcommunication with the ChemFET(s). In such an instance, the processormay be configured to perform one or more of: (i) generating a referenceI_(d)-V_(gs) curve, such as corresponding to the conductance of theChemFET channel(s), e.g., in the absence of a chemical reactionoccurring in the well and/or in proximity to the channel; and/or (ii)generating a chemical sensing I_(d)-V_(gs) curve in response to achemical reaction occurring in the well and/or in proximity to thechannel; and/or (iii) determining a difference, if any, between thereference I_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs)curve. Particularly for ambipolar channel nanomaterials such asgraphene, the difference between the reference I_(d)-V_(gs) curve andthe chemical sensing I_(d)-V_(gs) curve may be a shift in a Vgs value ofa minimum point of the chemical sensing I_(d)-V_(gs) curve relative to aVgs value of a minimum point of the reference I_(d)-V_(gs) curve.

Specifically, in one instance, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve may be ina shift in an Id value of a minimum point of the chemical sensingI_(d)-V_(gs) curve relative to an Id value of a minimum point of thereference I_(d)-V_(gs) curve. Additionally, the difference between thereference I_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curvemay be a shift in a final Id value of the chemical sensing I_(d)-V_(gs)curve relative to a final Id value of the reference I_(d)-V_(gs) curve.Further, the difference between the reference I_(d)-V_(gs) curve and thechemical sensing I_(d)-V_(gs) curve may be a shift in a parameter of thereference I_(d)-V_(gs) curve with a corresponding parameter of thechemical sensing I_(d)-V_(gs) curve, such as where the parameter is aslope, optionally a steepest slope, of the reference I_(d)-V_(gs) g andchemical sensing I_(d)-V_(gs) curves.

In some instances, the accuracy or sensitivity of the ChemFET detectionor analysis maybe be improved by combining one or more of the previouslydescribed techniques.

As indicated, in various instances, an ion-selective permeable membranemay be provided, such as where the ion-selective permeable membrane maybe positioned within a chamber of a well and/or positioned above orotherwise proximate to the channel. In certain instances, theion-selective permeable membrane may include a polymer, such as composedof a perfluorosulphonic material, a perfluorocarboxylic material, PEEK,PBI, Nafion, and PTFE material. Alternatively, the ion-selectivepermeable membrane may include an inorganic material, such as an oxideor a glass. In some instances, an additional 2D transistor material maybe included, such as graphene that need not be electrically connected tothe channel nanomaterial.

Further, in certain examples, the ion-selective permeable membrane maybe applied by a spin-coating, anodization, PVD, sol gel method, and thelike. Furthermore, in certain instances, the ChemFET may include an iongetter material, such as where the ion getter material preferentiallysequesters ion species that are not relevant to a particular chemicalreaction to be detected, and optionally reducing noise in signals fromthe ChemFET, such as where the ion getter material may placed over adielectric layer forming the well or chamber and/or in proximity to thechamber opening and/or channel.

The disclosure will be better understood by reference to the followingExamples, which are intended to merely illustrate certain preferredexamples for practicing some aspects of the disclosure. The scope of theclaims is not to be considered limited thereto.

EXAMPLES Example 1 Manufacture of a 2D ChemFET

In some examples manufacturing a well for a 2D nanomaterial FET involvesan organic passivation layer or an inorganic passivation layer.

For a well with an inorganic passivation layer, PECVD oxide, LPCVDOxide, or LPCVD Nitride are preferred, at least for the nitride, as thefilm has a lower stress and less tendency to crack. Most of the welldepth is created by a photoresist pattern process and a plasma etch orRIE. The final amount of well depth can be created by a wet etchprocess, since in many cases the channel nanomaterial, such as graphene,may be easily damaged or destroyed by a plasma or RIE etch process butis insensitive to a wet etch process. An alternative is to deposit athin SiN layer, then a thick SiO2 layer. The SiO2 is patterned andetched with a highly selective etch, in a preferred example, SiN acts asan ESL. Then a final wet etch process is performed on the SiN from thebottom of the well. Yet another option is to use a low temperature TEOSoxide, which is a denser, less porous oxide for the passivation layer.It prevents uptake of contaminants or reaction materials in the oxidethat may affect results.

There are various methods for forming the oxide or other passivationlayer (35) and forming a well structure (38) over the graphene layer.One such process for forming the well of controlled depth is to use atimed plasma etch or an endpoint detection to stop at or near thegraphene layer or at or near the analyte or reaction-sensitive layer(34) if it is present, then finish with a wet etch process to remove thelast of the passivation material over the channel area. An alternativemethod is to first deposit a thin SiN layer or other ESL (74) prior topassivation deposition.

FIG. 37A depicts the ChemFET before the deposition of the ESL andincludes an analyte or reaction-sensitive layer (34) over the graphenechannel material (30) and FIG. 37B depicts the ChemFET after thedeposition of the ESL (74). FIG. 37C shows the ChemFET after thedeposition of a thick SiO2 passivation layer (35), and the subsequentpatterning and etching of the SiO2 layer using a plasma anisotropicetch—with the etching highly selective for the passivation layer (35)versus the ESL (74) resulting in the etch process stopping on the ESL(74). In the example depicted here, SiN acts as an ESL (74). Then, thefinal step involves wet etching the SiN layer or ESL (74) from thebottom of the well with an etchant that is highly selective to the ESLused and not damaging to either the graphene layer (30) or the analyteor reaction-sensitive layer (34), if there is one present, as shown inFIG. 37D.

For organic wells, one possible material is a photoimageable organicmaterial. In such examples, since organics tend to stick to 1D or 2Dnanomaterials, such as graphene, and are difficult to remove (and reducethe nanomaterial carrier mobility or dope the nanomaterial, such asgraphene) it is preferred to first put on a thin inorganic layer, e.g.,by Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD) orAtomic Layer Deposition (ALD) of an oxide or nitride or carbide. Aneasier and lower cost option is to spin on a thin layer of Spin On Glass(SOG), after which the organic material (e.g., polyimide or BCB) to formthe organic layer is spun on, followed by imaging, developing, andcuring. The protective oxide or nitride or carbide is then wet etched(use of dry etching may destroy or degrade the graphene component) afterthe organic layer has been patterned.

In an alternate example with inorganic passivation layers, shown inFIGS. 35A to 35C, silicon oxide (20) is etched, preferably with a plasmaor RIE dry etch process, to form a well below a top copper layer and thestarting surface of the passivation (21). The well is positioned betweena source (22) and drain (24) electrode prior to graphene transfer asshown in FIG. 35A. Next, the graphene layer (30) is placed on the waferand conforms somewhat to the well profile (37) (see FIG. 35B).Thereafter, the graphene layer is patterned to the desired size andconfiguration for the channel (30) and may be coated with an analyte orreaction sensitive sensing layer (34).

As shown in FIGS. 36A-D, nanoimprinting of polymer material such as SU8epoxide photoresist passivation (35) (or another suitable polymermaterial) may be used for ChemFET well formation. As shown in FIG. 36A,the mold (72) is aligned with the passivation polymer (35) and ChemFETchannels (30). In FIG. 36B the mold (72) is imprinted into thepassivation polymer (35). In FIG. 36C the mold (72) is removed, exposingthe wells (38) formed by the imprinting process. In FIG. 36D anyresidual resist (35) or residual polymer (35) at the bottom of the well(38) is removed.

Preferred methods for manufacturing a well formation for a 2Dnanomaterial FET includes depositing a passivation layer (35) on achannel (30) of a 2D nanomaterial FET of a ChemFET structure. Suchmethods also preferably include etching through the majority of thepassivation layer (35) with a first etching method to create a majorityof a well (38) disposed over the channel (30). These methods can alsoinclude a second etching of the remaining passivation layer (35) overthe channel (30) to expose the channel (30) or an analyte orreaction-sensitive layer (34) within the well (38).

The 2D nanomaterial is selected from any suitable material, includinggraphene, silicene, molybdenum disulfide, black phosphorous(phosphorene), borophene, tungsten disulfide, boron nitride, tungstendiselenide, stanene, germanane, nickel HITP, and/or metaldichalcogenides or Mxenes such as Ti2C, (Ti0.5,Nb0.5), V2C, Nb2C, Ti3C2,Ti3CN, Nb4C3, or Ta4C3.

The semiconductor device structure is preferably based on FET, BJT, HBT,or any other transistor technology.

The semiconductor device structure is preferably based on CMOS, BiCMOS,bipolar, or other semiconductor fabrication technology.

In preferred examples, the passivation layer (35) is included of aninorganic material, such as an oxide, a nitride, a carbide, anoxy-nitride, a carbon-doped oxide, or a fluorine-doped oxide material.In other examples, the passivation layer is composed of an organicmaterial, such as a polymer, such as polyimide, BCB or PBO. In yet otherexamples, the passivation layer is composed of both inorganic andorganic materials.

The passivation layer is preferably deposited by a CVD, PECVD, PVD, orALD process.

The first etching method is preferably a plasma or laser etching method.A preferred plasma etching method is an RIE, HDP, ICP, or ECR method.The first etching method is performed through a mask material that ispatterned to shield parts of the passivation dielectric layer from thefirst etching method while having openings that expose other parts ofthe passivation dielectric layer to the first etching method, suchopenings generally aligned with ChemFET sensor locations. A preferredmask material is a photoresist or a hard mask material. Alternatively,the first etching method is predominantly an anisotropic etching method,and the second etching method is predominantly an isotropic etchingmethod.

Preferably, the second etching method is a wet or gaseous etchingmethod, such as an electrochemical or chemical etching method. Anexample of a chemical etching method is an acid, an aqueous acidsolution or a buffered acid solution. Preferably, the second etchingmethod etches the passivation layer without substantially etching oraffecting the channel nanomaterial.

In one exemplary preferred example, the passivation layer is included ofa first thin layer of material forming an etch stop layer (ESL) over thechannel and a second thicker layer of passivation material over the ESL.The first etching method has high selectivity for etching the secondthicker layer of passivation material as compared to the first thinlayer of ESL material. The first thin layer of ESL material ispreferably 0.1 nm to 100 nm thick and the second thicker layer ofpassivation material is preferably 0.1 μm to 10 μm thick. The first thinlayer of ESL material is preferably included of a silicon nitride or asilicon carbide. The first layer of thin ESL material may be included ofa non-stoichiometric material. The first etching method etches throughthe second thicker layer of passivation material and stops on the firstthin layer of ESL material.

Preferably, the first etching method etches through a controlled depthin the passivation material layer wherein the control is provided by atime of etching in conjunction with the rate of etching. Alternatively,control can be provided by an end point detection.

Preferably, the shape of the well formation when viewed from the top isa round or polygon shape.

Preferably, the largest width of the well formation when viewed from thetop is 0.1 μm to 10 μm.

Preferably, an array of two or more well formations are formed. Theratio of the pitch of two well formations to the largest width of thewell formations when viewed from the top is greater than 1 and less than10. The variation of the largest widths of the well formations whenviewed from the top in an array designed to have well formations withthe same largest widths is less than 10%.

Alternatively, the shape of the well formation is chosen with respect toconsideration of fluid dynamics of a fluid flowing over or into the wellformation. The consideration of fluid dynamics includes transport ofreagents or particles or microbeads over or into the well formation.

Other examples concern methods for manufacturing a well formation for a1D or 2D nanomaterial FET with an organic passivation layer. Thesemethods typically include depositing an organic passivation layer on achannel of a 1D or 2D nanomaterial FET of a semiconductor devicestructure. Such methods also include patterning the organic passivationlayer to create well formation locations over the channels. The methodsalso include removing the passivation layer over each channel to exposethe channel within the well formation.

The patterning of an organic passivation layer is preferably by aprinting method. The passivation layer is included of a photosensitivematerial and the patterning is by a photolithographic method. Theremoving is preferably by a developing method.

The organic layer is preferably a polymer such as polyimide, BCB,photoresist, PBO or parylene.

In such examples, the removing is preferably by an etching or adeveloping method such as a wet or gaseous etching or developing method.An example of wet or gaseous etching or developing method is anelectrochemical or chemical etching or developing method. The chemicaletching or developing method includes a base material, a photoresistdeveloper, KOH, TMAH, NaOH or other material suitable for etching ordeveloping the target passivation material.

In one example, the removing method is predominantly an isotropicetching or developing method. In another example, the removing method ispredominantly an anisotropic etching or developing method. The removingmethod etches or develops the passivation layer without substantiallyetching or affecting the channel nanomaterial.

The passivation layer is included of a first thin layer of materialforming an etch or developing stop layer over the channel and a secondthicker layer of material over the etch stop layer. The first etching ordeveloping method has high selectivity for etching or developing thesecond thicker layer of material as compared to the first thin layer ofmaterial.

Example 2 Manufacture of a GAA ChemFET

A preferred representative method for manufacturing a FET for chemicaland biological analysis is shown in FIGS. 10A-10C. The method includesdepositing a graphene channel on an exposed metal layer of an integratedcircuit structure (see FIG. 10A). The integrated circuit structureincludes a semiconductor substrate, a dielectric layer, and the metallayer. The method also includes utilizing a patterned material to exposea portion of a channel area and a plurality of adjacent areas. Themethod also includes etching the dielectric material starting with theadjacent areas thereby exposing a trench under the channel and exposingthe metal in the channel area. The method also includes etching themetal from underneath the graphene channel to create a ChemFET.

This method uses a full CMOS wafer with top copper electrodes exposed byCMP. In this case there is also copper in the channel area (26). Agraphene layer (30) is deposited (e.g., via PECVD or another suitablemethod) on all of the exposed copper areas. Then a pattern photoresistprocess is performed to pattern the channel areas. A furtherphotolithographic process is used to protect most of the wafer surfacebut to pattern and expose some areas near the central portions of thechannel and extending somewhat farther than the channel width, i.e.,exposing the silicon oxide (20) surface (21) nearby the channel (30) orto the side of the channel. Then SiO2 is etched from the sides of thechannel to expose a trench under the channel and expose the copper inthe central channel area (26). Then, the copper is wet-etched fromunderneath the graphene channel.

Advantages of this method include: no graphene release and layertransfer. The metal can be any suitable material (or combinations ofmaterial) for graphene growth, for example, Ni, Cu, Ru or Pt. Thegraphene layer can be deposited by CVD, PECVD, or any suitable process.Since semiconductor transistors have already been formed in the IC waferthe graphene deposition process must be limited to about 400 C or lessso as not to damage the semiconductor, e.g., CMOS, transistors. Thedielectric material can be an oxide, nitride, carbide, or low Kdielectric. The dielectric layer can be etched by a dry or wet,preferably predominantly anisotropic, etching process, although theselectivity of the etching process is targeted for the dielectric ormetal constituents as compared to the graphene (or any functional layerplaced over the graphene).

The patterned material is preferably a photoresist. The photoresist ispreferably patterned using a photolithographic process.

The semiconductor substrate is preferably a Si, SiGe, or a III-Vmaterial.

The integrated circuit is preferably formed using a CMOS, BiCMOS,bipolar, or other fabrication technology.

The semiconductor integrated circuit is preferably based on FET, BJT,HBT, or other transistor technology.

Etching the dielectric preferably includes a wet etching process, sincedry etching, e.g., plasma, processes are known to damage graphene.

Etching the dielectric preferably includes a wet or gaseous etchingmethod. The wet or gaseous etching method is preferably anelectrochemical or chemical etching method. The chemical etching methodpreferably includes an acid, an aqueous acid solution or a buffered acidsolution.

Etching the dielectric preferably includes predominantly an isotropicetching method. Etching the dielectric alternatively etches thedielectric without substantially etching or affecting the channelnanomaterial.

Etching the metal preferably includes a wet or gaseous etching method,wherein the wet or gaseous etching method is an electrochemical orchemical etching method, and wherein the chemical etching methodincludes an acid, an aqueous acid solution or a buffered acid solution.

Etching the metal alternatively includes predominantly an isotropicetching method.

Etching the metal alternatively etches the metal without substantiallyetching or affecting the channel nanomaterial.

The dielectric layer is preferably composed of a first thin layer ofmaterial forming an ESL under the channel to limit the extent of thedielectric etching. The dielectric etching has high selectivity foretching the dielectric material as compared to the ESL. The first thinlayer of material is preferably 0.1 nm to 100 nm thick. The first thinlayer of material is preferably composed of a silicon nitride, or asilicon carbide. The first layer of thin material is alternativelycomposed of a non-stoichiometric material.

Alternatively, the ESL may be configured in a tub-like configuration tomore fully restrict the etching of the dielectric material.

One or more functional layers are preferably deposited over the graphenechannel prior to etching the dielectric. Alternatively, one or morefunctional layers are deposited over the graphene channel subsequent toetching the dielectric. Etching the dielectric includes a wet or gaseousetching method, wherein the wet or gaseous etching method is anelectrochemical or chemical etching method, and wherein the chemicaletching method includes an acid, an aqueous acid solution or a bufferedacid solution. Etching the dielectric preferably includes predominantlyan isotropic etching method. Etching the dielectric etches thedielectric without substantially etching or affecting the channelnanomaterial and without substantially etching or affecting thefunctional material. Etching the metal includes a wet or gaseous etchingmethod, wherein the wet or gaseous etching method is an electrochemicalor chemical etching method, and wherein the chemical etching methodincludes an acid, an aqueous acid solution or a buffered acid solution.

Alternatively, etching the metal includes predominantly an isotropicetching method. Alternatively, etching the metal etches the metalwithout substantially etching or affecting the channel nanomaterial andwithout substantially etching or affecting the functional material.

Example 3 Nanomaterial Layer Transfer by Fusion Bonding

FIG. 21 shows a flow chart of a general method of forming asemiconductor wafer with transistors having 2D nanomaterial layers. Akey process step is the transfer of the 2D nanomaterial, such asgraphene, from a growth substrate to the target substrate, such as aROIC wafer. Discussed elsewhere are a variety of different transfertechniques that generally use some release method to release thegraphene from its growth substrate and a temporary bonding method, suchas adhesive bonding of the graphene to a carrier and then Van der Waalsbonding of the graphene to the target wafer with a subsequent secondrelease step, such as by thermal, laser or UV energy to release theadhesive and carrier wafer from the graphene. These transfer processesthat require temporary bonding and direct or indirect contact to thegraphene layer are not optimal as they open many opportunities fordefects in the graphene. A preferred approach uses direct transferfusion bonding of oxide, such as silicon dioxide layers, as illustratedin FIGS. 23A-23F.

FIGS. 23A-23F visually show the steps of direct bond transfer via fusionbonding. In the direct transfer fusion bonding process, the 2Dnanomaterial (530), e.g., graphene, is encapsulated with SiO2 (520)while it is still on the growth wafer and then the growth wafer may befusion bonded to a properly prepared CMOS ROIC wafer. Platinum,ruthenium, silver, copper, or another suitable metal may be used forgrowing the 2D nanomaterial (530) on the growth substrate. A release orseparation mechanism (e.g., bubble process) is used to separate the 2Dnanomaterial (530) from the platinum or other metal (528). The growthwafer may be a silicon, sapphire (Al2O3), or other suitable substratecapable of sustaining high temperatures with low thermal expansion.

In FIG. 23A, the 2D nanomaterial (530), preferably graphene, is grown ona growth platform included of a platinum layer (528) on a growth wafer(510).

In FIG. 23B, a cover material of silicon oxide is deposited on the 2Dnanomaterial and then the oxide is polished or CMP'ed to provide a veryflat and smooth surface on the silicon oxide.

In FIG. 23C, the growth platform is flipped.

In FIG. 23D, a ROIC wafer is prepared by polishing or CMP'ing a topmostsilicon oxide layer to provide a very flat and smooth surface on thesilicon oxide. The ROIC wafer and the growth platform are aligned forbonding.

In FIG. 23E, the silicon oxide cover material (520) is bonded to theROIC wafer topmost silicon oxide layer (520) through a fusion bondingprocess.

In FIG. 23F, the growth substrate is separated from the ROIC wafer,leaving the 2D nanomaterial (530), preferably graphene, on the ROICwafer, i.e., the process effectively transfers the 2D nanomaterial fromthe growth substrate to the ROIC wafer via fusion bonding. In the directtransfer fusion bonding process, the 2D nanomaterial, preferablygraphene, is encapsulated with SiO2 effectively protecting it fromhandling and process damage, and then the growth wafer is fusion-bondedto a CMOS ROIC wafer.

Platinum, copper, or another suitable metal is used for growing the 2Dnanomaterial (530). A release or separation process (e.g., a bubbleprocess) is used to separate the 2D nanomaterial (530) from the platinumor other metal (528). The growth wafer is preferably silicon, sapphire(A1203), or another suitable substrate capable of sustaining hightemperatures with low thermal expansion. Alternatively, a wafer formatis replaced with a panel or sheet. Various encapsulating materials areutilized such as SiO2, Si, Si3N4.

FIGS. 24A-24H show a variation the fusion bonding process, in this caseusing the process to first coat the graphene with an analyte orreaction-sensitive layer, such as an ion sensitive oxide layer, and thenbonding this ion sensitive oxide layer to a carrier wafer. Releasing thegraphene from the growth substrate and fusion bonding are similar to thepreviously described process, but the resultant final structure isdifferent since the ion sensitive oxide layer is integral to the finallayer stack—thus both the graphene layer and the ion sensitive oxidelayer are transferred by fusion bonding using this process.

In FIG. 24A, the 2D nanomaterial (530), preferably graphene, is grown ona growth platform included of a platinum layer (528) on a growth wafer(510).

In FIG. 24B, an ion sensitive oxide material is deposited on the 2Dnanomaterial.

In FIG. 24C the ion sensitive oxide is releasably joined to a carrierwafer.

In FIG. 24D the growth substrate has been removed (e.g., by a bubblerelease process or other means) exposing the graphene.

In FIG. 24E, a cover material of silicon oxide is deposited on the 2Dnanomaterial and then the oxide is polished or CMP'ed to provide a veryflat and smooth surface on the silicon oxide.

In FIG. 24F, the carrier platform is flipped and aligned with apreviously prepared ROIC wafer (e.g., CMP and/or polished SiO2 surface).

In FIG. 24G, the silicon oxide cover material (520) is bonded to theROIC wafer topmost silicon oxide layer (520) through a fusion bondingprocess.

In FIG. 24H, the carrier is separated from the ROIC wafer, leaving the2D nanomaterial (530), preferably graphene, covered with the ionsensitive layer (on the ROIC wafer, i.e., the process effectivelytransfers the 2D nanomaterial from the growth substrate to the ROICwafer via fusion bonding. In the direct transfer fusion bonding process,the 2D nanomaterial, preferably graphene, is encapsulated with SiO2effectively protecting it from handling and process damage, and then thegrowth wafer is fusion-bonded to a CMOS ROIC wafer.

FIG. 25 shows a wafer undergoing a bubble release process wherebygenerated gas bubbles are intended to gently force the graphene layerfrom its growth substrate. In practice this may be difficult to do sinceit is problematic to contact the thin film used on the growth substrate(it is both thin and covered by graphene). To make electricallycontacting the growth wafer easier a TSV 43 can bring an electrical pathfrom the thin film on the growth side of the wafer trough the wafer to aconductive layer on the backside of the wafer. It is easy to access thebackside of the wafer for electrical contact

Example 4 Improved Signal, Reduced Noise ChemFET

A preferred example of the disclosure is shown in FIG. 8. The disclosureprovides several enhancements to a graphene-based ChemFET sensor. In anenhancement example, the ChemFET is fabricated on an integrated circuitwafer and includes a first structure, a channel (30) and a secondstructure. A processor (not shown) is either included in the ChemFETsensor IC chip, e.g., fabricated from CMOS transistors, or is coupled tothe ChemFET IC chip. The first structure includes a conductive source(22) and a conductive drain (24). The channel (30) extends from theconductive source to the conductive drain, with the channel included ofa one-dimensional nanomaterial or a two-dimensional nanomaterial.

The processor is configured to generate a reference I_(d)-V_(gs) curveand a chemical sensing I_(d)-V_(gs) curve in response to a chemicalreaction, and analyte or biologic activity that is to be detectedoccurring over or near the ChemFET. The processor is also configured todetermine a difference between the reference and chemical sensingI_(d)-V_(gs) curve (or a parameter, e.g., slope, associated with suchcurves). The second structure enhances the ability of the processor todetermine the difference. The second structure may be an ion-selectivepermeable layer or an ion getter or a charge trap screening layer or alocal backgate, each of which will be described herein.

One enhancement example is an ion-selective permeable membrane (40) overthe channel (30) and analyte or reaction sensitive layer (34), ifpresent, that only allows ions of interest, such as hydrogen ions (68),to travel through the membrane. One preferred ion-permeable material isan inorganic material such as an oxide. An alternative material is aseparate layer of graphene that is note electrically connected to theFET. Another alternative material is a polymer such Nafion, PEEK, aperfluorosulphonic or a perfluorocarboxylic material.

Another alternative enhancement is a charge trap screening layer (42)under the graphene channel (30) that screens the graphene channel (30)from charges trapped in the dielectric layer (20), which is typically asilicon dioxide layer. The charge trap screening layer (42) may beformed of a polymer, such as HMDS, or other siloxanes or parylenes. Thecharge trap screening layer (42) may also be formed of an inorganicmaterial, such as aluminum oxide or most preferably hexagonal boronnitride (hBN). hBN has a lattice parameter very similar to graphene'slattice parameter (about 2.5 angstroms) and is also very smooth, both ofwhich factors attenuate any charge trapping between the graphene channel(30) and the charge trap screening layer (42) and lead to higher carriermobility in the channel (30). The thickness of the charge trap screeninglayer (42) may be 100 nm, or 75 nm, or 50 nm or less.

Yet another alternative enhancement is a getter material (41) elsewhereon the ChemFET sensor IC chip (1) or in the package to attract andsequester unwanted ions so that their interaction with the sensor can bereduced or eliminated and thus the determination of the sensor reactionto the desired ion is improved.

The second structure is preferably included of an ion-selectivepermeable membrane (40). The ion-selective permeable membrane allowsions of interest, e.g., H+ ions, to pass through the membrane whileblocking the passage of other ion species. The action of passing onlyions of interest through the membrane enhances the ability of theprocessor to determine the difference between the reference and chemicalsensing I_(d)-V_(gs) curves (or a parameter, e.g., slope, associatedwith such curves) and thus enhances the ability of the processor todetect the desired chemical reaction, analyte, or biologic activity(which is responsible for liberating the ion species of interest forsubsequent detection).

The ion-selective permeable membrane (40) is preferably included of apolymer such as perfluorosulphonic material, a perfluorocarboxylicmaterial, PEEK, PBI, Nafion or PTFE, although the membrane type willvary depending upon the chemical reaction and ion species desired to bedetected.

Alternatively, the ion-selective permeable membrane (40) is composed ofan inorganic material such as an oxide or a glass.

The ion-selective permeable membrane is preferably applied by aspin-coating, anodization, PVD, or sol gel method, which method may varydepending upon the chemical composition of the membrane to be applied.

Alternatively, the ion-selective permeable membrane (40) can be composedof a 2D nanomaterial, such as graphene, that is not electricallyconnected to the channel (30).

In one example, an ion-selective permeable membrane (40) can bepositioned over an ion sensitive layer (34) that is over the channel(30).

In an alternative example, the second structure is composed of an iongetter material (41), wherein the ion getter material (41) traps orsequesters ions (69) that are not relevant to the chemical reaction tobe determined and thus reduces unwanted signal or noise effects of theChemFET. The action of trapping ions (69) that are not relevant to thechemical reaction to be determined enhances the ability of the processorto determine the difference between the reference I_(d)-V_(gs) andchemical sensing I_(d)-V_(gs) curves (or a parameter, e.g., slope,associated with such curves) because there are fewer interfering ions(69) and thus enhances the ability of the processor to detect thedesired chemical reaction. Preferably, the ion getter material (41) isarranged proximate to the channel (30), such as on the sidewall (39 a or39 b) of the well (38), so that the action of “getting” the unwantedions improves the detection capability of the ChemFET of the disclosure.

Alternatively, the ion getter material (41) can be placed over adielectric layer in proximity to one or more of the channels. The iongetter material (41) may be a metal such as a barium or zirconium alloy,or preferably is a glass such as phosphorous-silicate glass (PSG),argon-silicate glass or arsenic-silicate glass. These getter materialsmay be especially adept at trapping sodium ions, which may be presentdue to the buffers used in the fluid. A preferred ion getter material(41) is a 4 to 8% by weight phosphorous-silicate glass (PSG) that isdeposited by a CVD process to a thickness of about 10 to 30 nm.

In another example, the second structure is included of a material tomanage the interaction of the 2D transistor channel (30) with anunderlying oxide dielectric layer (20) i.e., the second structure, is acharge trap screening layer (42). In such an example, the material maybe included of a polymer such as HMDS, a siloxane or parylene orincluded of an inorganic material such as aluminum oxide or preferablyhexagonal boron nitride (hBN). If an hBN layer is used its thickness maybe 100 nm, or 50 nm or less.

In another example, the second structure is included of a 2D transistorchannel (30) with an ion-sensitive material (34) over the channel (30),wherein the material (34) is sensitive to ionic species that aredifferent from the ions associated with the chemical reaction to bedetected, and wherein the action of sensing ions that are different fromthe ions associated with the chemical reaction to be detected assists infiltering unwanted noise from signals sent from the biosensor.

A further enhancement example is a backgate for the ChemFET (1). In thisexample a dual gate configuration is preferred wherein the solution gateapplies a gate voltage from the top or upper side of the channel (i.e.,through a gate or reference electrode (66) in communication with thefluid (64) that fills the chamber (37), which fluid (64) is in contactwith or proximate to the channel (30) and a backgate that applies a gatevoltage from the bottom or backside of the channel. Dual-gate ChemFETs(1) have higher sensitivity than just solution-gated or just backgatedChemFETs (1), even in some cases exceeding the Nernst limit of 59 mV/pH.In one backgate example the backgate is a global backgate, meaning thatone backgate voltage is applied globally to all the ChemFETs (1) on theChemFET sensor IC chip (50), such as applying a voltage to theconductive base structure (10).

In a preferred example there is a local backgate (82) associated withthe channel (30) of each ChemFET (1). A local backgate (82) may have avoltage that is tailored for the ChemFET to which it is applied, so forexample multiple ChemFETs may have multiple different local backgate(82) voltages applied to them depending on the characteristics andcircumstances of each individual ChemFET (1). The local backgate (82)will typically be implemented in a portion of an interconnect layer andis included of interconnect material 25, such as polysilicon, aluminumor copper or other metal. The local backgate will be of approximatelysimilar area and shape to the outline of the channel to which itapplies.

Example 5

Analysis of I_(d)-V_(gs) Curves

As described above, the ChemFETs of the disclosure will find variousapplications, including as biosensors. In such biosensing applications,a ChemFET-based biosensor senses a desired reaction that can bedetected, for example, by using a processor to detect an alteration,e.g., a shift, in an I-V curve, for example, an I_(d)-V_(gs) curve thatexamines the relationship between the drain current Id and the voltagebetween the gate and the source Vgs, or a parameter of an I_(d)-V_(gs)curve, e.g., the curve's slope, corresponding to the ChemFET. In suchapplications, a processor functionally associated with the ChemFETpreferably compares a reference I-V curve for the well (or other captureregion or structure) and an I-V curve generated in connection with achemical reaction in the well (or other capture region or structureassociated with the ChemFET). If the processor detects a differencebetween the reference and reaction-associated curves that exceeds apredetermined threshold, a positive result can be indicated. Examples ofsuch curves are presented in FIGS. 13B-13I, while FIG. 13A illustratesvarious components and parameters of an I_(d)-V_(gs) curve

In an alternative example, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve is ashift in an Ion value of the chemical sensing Id-Vgs curve relative toan Ion value of the reference I_(d)-V_(gs) curve. The Ion shift can beevaluated in the n-type or p-type region of the curve if the curve isgenerated by an ambipolar nanomaterial such as graphene. See FIGS. 13E,13F.

In an alternative example, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve is ashift in an Ioff value of the chemical sensing Id-Vgs curve relative toan Ioff value of the reference I_(d)-V_(gs) curve. See FIG. 13G.

In an alternative example, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve is anoverall change in shape of the chemical sensing I_(d)-V_(gs) curverelative to an overall change in shape of the reference I_(d)-V_(gs)curve. See FIG. 13D.

In an alternative example, the difference between the referenceI_(d)-V_(gs) curve and the chemical sensing I_(d)-V_(gs) curve is achange in the slope of the chemical sensing Id-Vgs curve relative to achange in the slope of the reference I_(d)-V_(gs) curve. The change inslope can be evaluated in the n-type or p-type region of the curve ifthe curve is generated by an ambipolar nanomaterial such as graphene.See FIG. 13I.

The Ion values may be taken from the p-type section or the n-typesection of an I_(d)-V_(gs) curve. In a preferred example, the slopes ofthe reference and test curves are measured on the steepest sections onthe n-type portions of the I_(d)-V_(gs) curves, whereas in anotherpreferred example, the slopes of the curves can be measured on thesteepest sections on the p-type portions of the I_(d)-V_(gs) curves. Inyet another example, the slopes are measured on the steepest sections onboth the p-type and n-type portions of the reference and testI_(d)-V_(gs) curves. See FIG. 13I.

In some examples, the difference between a reference I_(d)-V_(gs) curveand a chemical sensing I_(d)-V_(gs) curve is an overall change in shapeof the chemical sensing (or test) I_(d)-V_(gs) curve relative to anoverall change in shape of the reference I_(d)-V_(gs) curve. Thedifference in overall shape of the I_(d)-V_(gs) curves can bedetermined, for example, by first fitting a polynomial or other fittingline to each of the I_(d)-V_(gs) curves and then comparing thecoefficients of those fitting lines. See FIG. 13H.

In some examples, the gate voltage, Vgs, of the I_(d)-V_(gs) curve is agate voltage applied to the chemically-sensitive field effect transistorof the disclosure.

In other examples, the gate voltage Vgs of the I_(d)-V_(gs) curve is aback gate voltage applied to a ChemFET through the back of the device.

In some another examples, the gate voltage of the I_(d)-V_(gs) curve isa top gate voltage applied to the ChemFET through the top of the device.

In yet other examples, the gate voltage of the I_(d)-V_(gs) curve is asolution gate voltage applied to the ChemFET through a solution over thedevice.

In some instances, the accuracy or sensitivity of the ChemFET detectionor analysis maybe be improved by combining one or more of the previouslydescribed techniques.

Although the curves shown in FIGS. 13A-13I are representative of anambipolar ChemFET channel nanomaterial, such as graphene, similar shiftsin I-V curves can be evaluated for other 1D or 2D ChemFET channelnanomaterials.

Example 6 Preparing FETs

Alternative methods for growing and transferring 2D nanomaterials aredescribed, for example, in Hoffman et al., U.S. Provisional PatentApplication No. 62/175,351, filed on Jun. 14, 2015, for System AndMethod For Growing And Transferring Graphene For Use As A FET, which ishereby incorporated by reference in its entirety.

FIGS. 34A-34M illustrate a preferred CMOS integration method forbuilding interconnects, dielectric, and well structures, as well as thepads for bonding the transferred 2D nanomaterial to the chip.

FIG. 34A illustrates a graphene on a ROIC wafer step of a CMOSintegration method. FIG. 34B illustrates a patterning a graphene layerto form channels step of a CMOS integration method. FIG. 34C illustratesa depositing an etch stop layer over a graphene layer step of a CMOSintegration method. FIG. 34D illustrates a deposit, pattern and etch ofa thick insulator layer step of a CMOS integration method. FIG. 34Eillustrates a wet etch ESL, pattern and DRIE oxide over interconnectsstep of a CMOS integration method. Not shown is an optional addition ofwork function matching material prior to a via fill step of a CMOSintegration method.

FIG. 34F illustrates a deposit a barrier, liner, copper plate, CMP stepof a CMOS integration method. FIG. 34G illustrates a deposit abarrier/adhesion layer, deposit aluminum, pattern, etch aluminuminterconnect and pad layer step of a CMOS integration method. FIG. 34Hillustrates a deposit of passivation material such as silicon oxide orsilicon nitride (e.g., by CVD or PECVD) and pad open etch step of a CMOSintegration method. FIG. 34I illustrates a DRIE well insulator down toan etch stop layer step of a CMOS integration method. FIG. 34Jillustrates a wet etch (with a liquid or gaseous etchant) of a thin etchstop layer step of a CMOS integration method.

The substrate may be composed of at least one of Si, Si/SiO2, SiO2,sapphire/Al2O3, and a metal plate. An adhesion layer, as needed, iscomposed of at least one of Ti, Cr, Ta, W, WN, and TaN. The adhesionlayer has a thickness of 5 to 200 angstroms and preferably approximately100 angstroms. The metal layer is formed by at least one of PVD(sputtering, ebeam evaporation, thermal evaporation), CVD,electrochemical plating, and ALD.

Optional surface polishing, e.g., mechanical polishing,electropolishing, or CMP, after metal deposition is performed. Also, anoptional plasma treatment (best done just before growth) with plasmawith H2 and N2 or ammonia at approximately 0.1 Torr, 300-400 C can beperformed.

An analyte or reaction-sensitive layer (not shown) could be depositedover the channel and prior to deposition of the ESL. In other examplessuch an analyte or reaction-sensitive layer could act as the ESL, inwhich case there would be no wet etch of this layer as was describedwith respect to FIG. 34J.

Example 7

Sensor Stacked with Other IC Chips

FIG. 15B depicts a ChemFET sensor IC chip (50). Such an IC chip includesone or more ChemFET sensors, as previously described, and Read-OutIntegrated Circuits (ROIC), access transistors (11) or other circuitryare formed in the lower semiconductor portion of the IC chip usingnormal semiconductor transistors, such as CMOS transistors. Althoughsome amount of ROIC, signal processing, processor or other circuitry maybe included in the ChemFET sensor IC chip (50) it may be the case thatnot all the circuitry needed for sensor signal detection and processingand data storage is able to be included on the ChemFET sensor IC chip(50) due to practical limitations with the size of the chip and thenumber of semiconductor transistors that may be integrated on the chipdue to wafer fabrication limits.

In such a case the ChemFET sensor IC chip would normally communicateeither with other IC chips (such as a processor or memory chip) or witha computing system in order to perform the detection and analysisfunctions required, wherein typically these other IC chips would belocated on a printed circuit board embedded in a system. In one exampleof the instant disclosure, other IC chips can be bonded directly to theChemFET sensor IC chip and by doing so improved electrical performance(faster operation and lower power) may be achieved since theinterconnect length between the chips can be drastically reduced.Furthermore, the overall size of the solution (ChemFET sensor IC chip,processor chip(s), memory chip(s) or others) may be significantlyreduced, as well as reducing the size of any system that includes thosechips.

FIG. 16 depicts a stacked arrangement of IC chips, including a ChemFETsensor IC chip (50), a processor IC chip (52), a memory controller ICchip (54) and a memory IC chip (56). Physical and electricalcommunication between the IC chips is provided by Through Silicon Vias(TSVs) (43) and connections members (44), such as solder joints.

Example 8 Sensor IC Chip Stacked to Create Flow Channels

FIGS. 57A-C depict various methods of physically stacking ChemFET sensorIC chips (50) to create fluid flow channels between the ChemFET sensorIC chips (50) to create fluid flow channels between the ChemFET sensorIC chips (50). Stacking of the ChemFET sensor IC chips (50) can havemultiple benefits, one of which being that without increasing the areataken up by the sensor chip and with minimal increases in the verticaldistance (due to the chip stacking) the number of sensors can beincreased significantly (2 times for 2 stacked chips, 3 times for 3stacked chips, etc.). This is of benefit because larger numbers ofsensors can lead to overall improved detection accuracy since there aremore detection signals to combine and a statistically more accuratedetection can be made. Furthermore, sensor chip stacking allows largerChemFET sensors to be used, which have lower noise and therefor betterdetection sensitivity, while still fitting in a small volume.

The stacked ChemFET sensor IC chips (50) can be of the same design(e.g., identical copies of each other) or they may be of differentdesigns, for example optimized to detect different analytes, chemicalreactions, or biologic activity. A stacked combination of differentChemFET sensor IC chips (50) can make detection of a target much moreefficient since one fluid flow or sample exposure to the stacked chipscan allow simultaneous sensing or detection of different analytes,chemical reactions or biologic activity that may be associated with thefluid or sample. Furthermore, if different ChemFET sensor IC chips areused in the chip stack they may not only be of different design, butthey may have ChemFET sensors based on different nanomaterials, e.g.,one chip may have gFET sensors and another chip may have Si NW sensors.In this fashion the chips may be further optimized for differentpurposes yet used simultaneously for detection or sensing when includedin the same chip stack.

FIG. 17A depicts a stack of two ChemFET sensor IC chips, oriented faceto face. Physical connection members (45) hold the chips in properorientation and may also be used to define flow channels between theChemFET sensor IC chips (50).

FIG. 17B depicts a stack of two ChemFET sensor IC chips, oriented faceto face. The chips are held in proper orientation by an external means(not shown) and thus the fluid flow between the chips is not restrictedby physical connection members.

FIG. 17C depicts a stack of two ChemFET sensor IC chips, each orientedin the same direction, e.g., face up. Physical connection members (45)hold the chips in proper orientation and may also be used to define flowchannels between the ChemFET sensor IC chips (50). A lid (47), such as apackage lid, defines the fluid flow area for the topmost ChemFET sensorIC chip (50).

FIG. 16 depicts a stacked arrangement of IC chips, including a ChemFETsensor IC chip (50), a processor IC chip (52), a memory controller ICchip (54) and a memory IC chip (56). Physical and electricalcommunication between the IC chips is provided by Through Silicon Vias(TSVs) (43) and connections members (44), such as solder joints.

Example 9 Gate all Around Structures

A typical nanomaterial-based ChemFET (1), such as depicted in FIG. 3Ahas a conductive source (22), a conductive drain (24), a nanomaterialchannel (30) such as graphene, a well structure (38) and associatedchamber (37), a fluid (64) and a gate voltage applied through the fluid(64) such as applied by a gate or reference electrode (66) in order toform a nanomaterial-based, solution-gated ChemFET (1). The ChemFET (1)may In some instances, include an analyte or reaction-sensitive layer(34), which may further improve the sensitivity of the ChemFET (1) fordetection of certain analytes or chemical reactions or biologicactivity.

An improvement over the typical ChemFET (1) just described to is providea second gate, i.e., a backgate for the device such that the backgateand solution gate can both apply voltages to the channel in a dual-gatefashion. Having two gate voltages, on opposite the other around thechannel (30) has the advantage of more precisely controlling the ChemFETwhich in turn leads to better sensor sensitivity.

An even more enhanced example of this concept is to completely surrounda portion of the channel with gate material so that the whole channelcircumference in some portion of the channel is fully enclosed by thegate material. This gives the highest degree of control over the channelthrough the gate all around structure.

FIGS. 9C and 9D depict a side sectional view and a top-down view,respectively, of a gate all around ChemFET (1) included of a conductivesource (22), conductive drain (24), channel (30) such as a graphenechannel, an optional analyte or reaction-sensitive layer (34) over thechannel (30), a well structure (38) providing a chamber (37) that holdsa fluid (64) wherein a gate or reference electrode (66) applies a gatevoltage to the fluid. In the gate all around example the dielectric andmetal under a relatively large portion of the channel region have beenremoved, such as by etching. In this fashion the fluid (64) is free toflow over, under and around the exposed portion of the channel—henceforming a gate all around structure.

In one instance the gate all around structure is achieved by providingan etch stop structure (74) configured as a tub-like shape andpositioned in the dielectric material (20) under the channel (30) asshown in FIG. 9A. FIG. 9B depicts the ChemFET (1) after the wellstructure (38) has been formed and after the dielectric (20) under thechannel and within the etch stop layer-defined tub has been etched away.In this example the etch is preferably a wet chemical etch and not adry, e.g., plasma, etch since dry etch processes tend to damage ordestroy the graphene. A suitable wet etchant is a hydrofluoric (HF)acid-based etchant, such as a mixture of HF and a buffer such asammonium fluoride. This etchant has high selectivity to silicon dioxidein comparison to silicon and thus silicon of the sensor IC chip wafershould not be damaged. Furthermore, an HF-based etch should not have badeffect on the graphene channel (30).

In a second instance of the preferred gate all around structure, thegraphene is first deposited or formed on a metal interconnect material(25) that may form one of the source (22) or drain (24) conductiveelectrodes as shown in FIG. 10A. If the interconnect material is copper,such as formed in trenches in a damascene process and with the upperportions of the electrodes exposed to the surface, i.e., copper isexposed to the surface then the possibility exists for forming thegraphene (i.e., growing the graphene) directly on the semiconductor ICwafer rather than on a separate growth wafer and then transferring thegraphene to the IC wafer. This may be possible since copper is one ofthe preferred growth substrates for graphene (graphene does not diffuseinto copper during the growth) and if the growth temperature is kept lowenough, such as lower than 400 C, so as not to affect the semiconductortransistors, such as CMOS transistors.

A plasma-enhanced CVD (PECVD) or other enhanced CVD process may allowgrowth of good quality graphene directly on the exposed copper surfaceson an IC wafer. Once the graphene is formed or deposited on the copperareas, such as shown in FIG. 10A then in a subsequent process step thedielectric underlying the channel area (26), which at this time includesboth graphene and a thin layer of copper, is etched. For a silicondioxide dielectric, a wet HF acid etchant is suitable. The etch may befurther controlled or confined by an etch stop layer (74) formed in atub-like shape. As depicted in FIG. 10B. Finally, the thin copper layerunder the graphene channel (30) can be etched by a suitable copperetchant, such as ammonium persulfate or ferric chloride, resulting inthe central portion of the graphene channel to be free of anydielectric, as shown in FIG. 10C, and available for contact by the fluidto form a gate all around structure as shown in FIG. 9C.

In another gate all around example, as shown in FIG. 11A, there is noetch stop layer provided under the channel sensing region (26). In thiscase the wet etching of the silicon dioxide dielectric (20) will beisotropic and will result in a bowl-shaped cavity beneath the channel(30) as shown in FIG. 11B. Furthermore, since the etching is notconfined by an etch stop layer, the etched cavity may not be fullyuniform in size and shape.

All of the process examples just discussed result in the preferred gateall around structure shown in FIG. 9C.

Example 10 Sealing of Chambers for Improved Sensing

FIG. 38A depicts a ChemFET sensor IC chip (50). During operation it isoften the case that an analyte to be detected, a biologic to bemonitored or a reaction to be detected will generate ions. For example,a base nucleotide incorporation onto a template DNA strand will releasea hydrogen ion. The ChemFET can be used to sense these ions. However, asshown in FIG. 38A the ions (62) are not confined and may travel throughthe fluid (64). This can cause problems if more ions appear in one well(38) than another well, resulting in a larger signal in one well versusthe other and possible leading to a false interpretation of the ChemFETsignal. In an ideal case the ions generated in a well would remainwithin that well.

In one example, FIG. 38B depicts a ChemFET sensor IC chip (50) whichincludes a moveable seal (90) shown in an upper or unsealed position.The seal may be raised up during times when fluid (64) needs to flowover the IC (50), such as when new reagents must be brought to theChemFETs. However, as soon as the flow is done the moveable seal may beplaced in a downward or sealed position as shown in FIG. 38C. In thiscase the reagents and resulting reaction products, such as ions, areconfined to their wells (38). This minimizes the chance for false signalgeneration and interpretation. Furthermore, the ions are moreconcentrated to the wells since none are flowing outside the well areasso the overall density of ions per well is increased from the normalsituation of FIG. 38A. This higher ion concentration will result inhigher signal strength and higher sensor sensitivity.

In another example, FIG. 38D depicts a ChemFET sensor IC chip (50) whichincludes barrier generators (92) at the top surfaces of each wellstructure (38). These barrier generators (92) are used to createelectromagnetic barrier fields (94) around the periphery of each well.For example, a positively charged electromagnetic barrier filed (94)could repel positively charged hydrogen ions (62) and thus confine themto their individual chambers (38). This confinement, similar to thediscussion above, results in higher ion concentration, improved signalstrength, and better sensor sensitivity.

The generation of the barrier field may need to be provided such thatthe field does not interfere with the ChemFET operation. For example,the barrier fields may be pulsed on and off. Pulsed on when the ions areto be confined and pulsed off when a read of a sensor is to be taken andthe read should not be disturbed by the barrier field. Alternatively,the barrier fields may be operated in such a fashion, such as operatedas high frequency AC fields, that any extraneous signals generated bythese barrier fields (94) during the ChemFET reading operation areeasily determined by signal processing techniques and are eliminatedfrom the readout.

In another example, FIG. 38E shows a ChemFET sensor IC chip (50) whichincludes a flow control member (96) which includes microvalves (98). Inthis example the flow control member (96) and associated flow controlmicrovalves (98) are fixedly attached to the top of the ChemFET sensorIC chip (50). Flow channels that bring reagents or analytes to each well(38) are controlled by the microvalves which can allow flow to thechambers when the microvalve is open or prevent flow to or from thewells when the microvalve is closed. The flow control member (96) andassociated microvalves (98) may be manufactured bymicroelectromechanical systems (MEMS) techniques. This may be necessarybecause the size of the wells on the ChemFET sensor IC chip (50) aresmall and the microvalves likewise need to be small. As with the otherexamples, when the wells are closed off by the microvalves (98) the ionsare concentrated in the wells resulting in higher sensor sensitivity.

Example 11 Read Latency Reduction and Accuracy Improvement

In a ChemFET sensor IC chip (50) a fluid is used to introduce analytesor flow reagents over the chip and into the wells (38) of each ChemFET.Ideally the reading of sensors would be timed so that reading occurs asa new fluid wavefront with new analyte or reagents flows over thosesensors, i.e., you want to read the sensors as the reactions are ongoingin their well (38).

The ChemFET sensors in the ChemFET sensor IC chip (50) are arranged inan array similar to an array of memory cells or an array of image sensorpixels. Likewise, wordlines and bitlines may be used on the ChemFETsensor IC chip (50) to access and read any individual ChemFET sensor(1). During a read operation, especially for large chips with manycells, there can be a delay or latency in the time needed to charge upthe bitlines before a read can occur of the desired sensor. Read latencycan be reduced by making the accessed bitlines (columns) shorter bysegmenting them (shorter lines can react faster to applied voltagechanges) and by precharging them (so that the bitline is already at theread/bias voltage prior to a read).

Furthermore, the concepts of bitline segmentation and precharging can becombined with the desire to read sensors only when the fluid wavefronthas recently passed that sensor location. These concepts can be combinedwith microfluidics control to segment the read areas on the ChemFETsensor IC chip (50) for higher accuracy and reduced latency.

One can use a microfluidics structure and control the flow analyte orreagent fluid flow segment by segment over the area of the ChemFETsensor IC chip (50). In concert with the fluid flow control, one canprecharge the bitlines for those segments to be read next, which arealso the segments that will see fluid flow next, to reduce read latency.Other tasks (address decoding, output driving) can be performedsimultaneously with the bitline precharging, either within the samesegment or in other segments to reduce latency. Also, in segments thatare not being read the bitlines can be turned off, or more accuratelytheir precharge circuits can be turned off, thereby reducing power.

FIG. 39 illustrates a ChemFET sensor IC chip (50) that includes a flowcontrol member (96) and associated microvalves (98 and 99). The ChemFETsensor IC chip (50) includes multiple ChemFET sensors and related wells(38) arranged in an array over the area of the chip (50). As previouslydescribed access to segments of sensors (e.g., columns) for a readoperation is done by toggling bitlines associated with those columns.Likewise toggling a wordline (row) in combination with a bitline allowsa specific individual sensor to be read (each sensor is at a unique rowand column location). The bitlines can be segmented so that only thebitlines in that segment need to be precharged and toggled for sensorsin that segment to be read. It is preferable to coordinate the reads ofthe sensor segments with the fluid (64) flow to those sensor segments.FIG. 39 shows a fluid control member (96) that is allowing fluid (64)flow only to the rightmost segment because the microvalves controllingfluid flow to that segment are open (99). Conversely the microvalves(98) controlling fluid flow to the leftmost and middle segments areclosed and therefore no fluid (64) is flowing to those segments).

Coordination of reading segments of sensors on the ChemFET sensor ICchip (50) by controlling fluid flow to be timed with read operations incertain segments will result in improved read accuracy since the readswill occur when fresh analyte or reagents have reached the sensors inthat segment. Such segmentation and coordination is provided by fluidcontrol members with microvalves and by bitline segmentation.

A useful detailed description is set forth in van Rooyen et al., U.S.Patent Publication Number 20140371110 for Bioinformatics Systems,Apparatuses, and Methods Executed On An Integrated Circuit ProcessingPlatform, which is “hereby incorporated by reference in its entirety.

A useful detailed description is set forth in van Rooyen et al., U.S.Patent Publication Number 20140309944 for Bioinformatics Systems,Apparatuses, and Methods Executed On An Integrated Circuit ProcessingPlatform, which is hereby incorporated by reference in its entirety.

A useful detailed description is set forth in van Rooyen et al., U.S.Patent Publication Number 20140236490 for Bioinformatics Systems,Apparatuses, and Methods Executed On An Integrated Circuit ProcessingPlatform, which is hereby incorporated by reference in its entirety.

A useful detailed description is set forth in van Rooyen et al., U.S.Patent Publication Number 20140200166 for Bioinformatics Systems,Apparatuses, and Methods Executed On An Integrated Circuit ProcessingPlatform, which is hereby incorporated by reference in its entirety.

A useful detailed description is set forth in McMillen et al., U.S.Provisional Patent Application No. 62/127,232, filed on Mar. 2, 2015,for Bioinformatics Systems, Apparatuses, And Methods Executed On AnIntegrated Circuit Processing Platform, which is hereby incorporated byreference in its entirety.

A useful detailed description is set forth in van Rooyen et al., U.S.Provisional Patent Application No. 62/119,059, filed on Feb. 20, 2015,for Bioinformatics Systems, Apparatuses, And Methods Executed On AnIntegrated Circuit Processing Platform, which is hereby incorporated byreference in its entirety.

A useful detailed description is set forth in van Rooyen et al., U.S.Provisional Patent Application No. 61/988,128, filed on May 2, 2014, forBioinformatics Systems, Apparatuses, And Methods Executed On AnIntegrated Circuit Processing Platform, which is hereby incorporated byreference in its entirety.

A useful detailed description of a gFET is set forth in van Rooyen, U.S.Provisional Patent Application No. 62/094,016, filed on Dec. 18, 2014,for Graphene FET Devices, Systems, And Methods Of Using The Same ForSequencing Nucleic Acids, which is hereby incorporated by reference inits entirety.

A useful detailed description of a gFET is set forth in Hoffman et al.,U.S. Provisional Patent Application No. 62/130,594, filed on Mar. 9,2015, for Chemically Sensitive Field Effect Transistor, which is herebyincorporated by reference in its entirety.

A useful detailed description of a gFET is set forth in Hoffman et al.,U.S. Provisional Patent Application No. 62/130,598, filed on Mar. 9,2015, for Method And System For Analysis Of Biological And ChemicalMaterials, which is hereby incorporated by reference in its entirety.

A useful method for growing and transferring graphene is disclosed inHoffman et al., U.S. Provisional Patent Application No. 62/175,351,filed on Jun. 14, 2015, for a System And Method For Growing AndTransferring Graphene For Use As A FET, which is hereby incorporated byreference in its entirety.

As A FET, which is hereby incorporated by reference in its entirety.

A use for 2D nanomaterials is disclosed in Hoffman et al., U.S.Provisional Patent Application No. 62/175,384, filed on Jun. 14, 2015,for a CMOS Integration Of A Two-Dimensional Material, which is herebyincorporated by reference in its entirety.

The following U.S. Patent Applications discuss the processing componentof the a system for analysis of biological and chemical materials: U.S.patent application Ser. No. 14/279,063, titled, Bioinformatics Systems,Apparatuses, and Methods Executed on an Integrated Circuit ProcessingPlatform, filed May 15, 2014; U.S. patent application Ser. No.14/180,248, titled Bioinformatics Systems, Apparatuses, and MethodsExecuted on an Integrated Circuit Processing Platform, filed Feb. 13,2014; U.S. patent application Ser. No. 14/179,513, titled BioinformaticsSystems, Apparatuses, and Methods Executed on a an Integrated CircuitProcessing Platform, filed Feb. 12, 2014; U.S. patent application Ser.No. 14/158,758, titled Bioinformatics Systems, Apparatuses, and MethodsExecuted on an Integrated Circuit Processing Platform, filed Jan. 17,2014; U.S. patent application Ser. No. 14/279,063; U.S. ProvisionalApplication No. 61/826,381, titled System and Method for ComputationGenomic Pipeline, filed May 22, 2013; U.S. Provisional Application No.61/943,870, titled Dynamic Genome Reference Generation For Improved NGSAccuracy And Reproducibility, filed Feb. 24, 2014; all of which arehereby incorporated by reference in their entireties herein.

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this disclosure andwill readily understand that while the present disclosure has beendescribed in association with a preferred example thereof, and otherexamples illustrated in the accompanying drawings, numerous changesmodification and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this disclosure which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claim. Therefore, the examples of the disclosure inwhich an exclusive property or privilege is claimed are defined in thefollowing appended claims.

All of the devices and methods described and claimed herein can be madeand executed without undue experimentation in light of the presentdescription. While the devices and methods of this disclosure have beendescribed in terms of preferred examples, it will be apparent to thoseof skill in the art that variations may be applied to the compositionsand methods. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit and scope ofthe disclosure as defined by the appended claims.

All patents, patent applications, and publications mentioned in thespecification are indicative of the levels of those of ordinary skill inthe art to which the disclosure pertains. All patents, patentapplications, and publications, including those to which priority oranother benefit is claimed, are herein incorporated by reference to thesame extent as if each individual publication were specifically andindividually indicated to be incorporated by reference.

The examples illustratively described herein suitably may be practicedin the absence of any element(s) not specifically disclosed herein.Thus, for example, in each instance herein any of the terms“comprising”, “consisting essentially of”, and “consisting of” may bereplaced with either of the other two terms. The terms and expressionswhich have been employed are used as terms of description and not oflimitation, and there is no intention that in the use of such terms andexpressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the claims. Thus, itshould be understood that although the present subject matter has beenspecifically disclosed by preferred examples and optional features,modification and variation of the concepts herein disclosed may beresorted to by those skilled in the art, and that such modifications andvariations are considered to be within the scope defined by the appendedclaims.

What is claimed is:
 1. An apparatus comprising: a biosensor integrated circuit (IC) chip comprising one or more sensing zones within one or more well structures configured to receive a liquid comprising one or more biological analytes; a passivation layer with an opening over a channel layer and comprising an array of graphene field effect transistors (gFETs), the individual gFETs comprising: a graphene channel formed in the channel layer and comprising a two-dimensional layer of carbon atoms, the graphene channel disposed on a dielectric oxide layer; a conductive drain connected at a first end of the graphene channel; and a conductive source connected at a second end of the graphene channel, wherein a liquid gate is formed above the top surface of the graphene channel upon receipt of the liquid; the biosensor IC chip further comprising: one or more reference electrodes formed in a metal layer of the biosensor IC chip and configured to contact the liquid, the one or more reference electrodes disposed at a horizontal distance apart from the graphene channels of the gFETs in the array, wherein: at least one of the one or more reference electrodes is configured to apply a liquid gate voltage to the liquid; and at least one of the one or more reference electrodes is configured to measure a liquid gate voltage of the liquid, wherein the individual gFETs and the first and second reference electrodes are operable to enable a set of measurements to be made to sense one or more parameters of a biological analyte in the liquid based on changes in a shape of a chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs), in response to the presence of the biological analyte in the liquid on or over the channels of the individual gFETs.
 2. The apparatus of claim 1, wherein the changes in the shape of the chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs) curves include transconductance slope changes.
 3. The apparatus of claim 2, wherein the transconductance slope changes include changes to transconductance slope in both a p-type region and an n-type region of the chemical sensing I_(d)-V_(gs) curve.
 4. The apparatus of claim 2, wherein the individual gFETs are configured to enable sensing of one or more parameters of the one or more biological analytes in the liquid based on shifts of a chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs).
 5. The apparatus of claim 4, wherein the shifts of the chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs) are selected from horizontal shifts, vertical shifts, or combinations thereof.
 6. The apparatus of claim 4, wherein the shifts of the chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs) include shifts in parameters selected from on current (I_(on)) in the p-type region, Dirac voltage (V_(Dirac)), on current (I_(on)) in the n-type region, and combinations thereof.
 7. The apparatus of claim 1, further comprising one or more capture regions on or over the channel of the one or more gFETs, the individual capture regions configured respectively to accommodate attachment of a selected biomaterial to a top surface of the graphene channel, the biomaterial selected to detect a biological analyte of the one or more biological analytes in the liquid.
 8. The apparatus of claim 1, wherein the biomaterials in the respective capture regions of the one or more capture regions are selected to detect analytes selected from ions associated with biomolecules, nucleic acids, antigens, polysaccharides, proteins, peptides, small molecules, and combinations thereof.
 9. The apparatus of claim 1, wherein at least a portion of the source electrodes and the drain electrodes have interdigitated geometries.
 10. The apparatus of claim 1, wherein the passivation layer provides an insulating layer between liquid and the regions at which the source electrode and the drain electrode connect to the graphene channel of the individual gFETs.
 11. The apparatus of claim 10, wherein the passivation layer comprises silicon nitride.
 12. The apparatus of claim 11, further comprising an ion permeable membrane disposed above the graphene channel and configured to allow selected ions to pass to the sensing region of the graphene channel.
 13. The apparatus of claim 1, further comprising flow channels that bring reagents and/or analytes to the one or more well structures.
 14. A system comprising: a biosensor integrated circuit (IC) chip having one or more well structures configured to receive a liquid comprising one or more biological analytes; sensing zones within the one or more well structures comprising a passivation layer with an opening over a channel layer and comprising an array of graphene field effect transistors (gFETs), the individual gFETs comprising: a graphene channel formed in the channel layer and comprising a two-dimensional layer of carbon atoms, the graphene channel disposed on a dielectric oxide layer; a conductive drain connected to a first end of the graphene channel; and a conductive source connected to a second end of the graphene channel, wherein the individual gFETs are configured such that the liquid received by the one or more well structures is confined to form a liquid gate above the top surface of the graphene channel; the biosensor IC chip further comprising: one or more reference electrodes formed in a metal layer of the biosensor IC chip and configured to contact the liquid, the one or more reference electrodes disposed at a horizontal distance apart from the graphene channels of the gFETs in the array, wherein: at least one of the one or more reference electrodes is configured to apply a liquid gate voltage to the liquid; and at least one of the one or more reference electrodes is configured to measure a liquid gate voltage of the liquid, wherein the individual gFETs and the first and second reference electrodes are operable to enable a set of measurements to be made to sense one or more parameters of a biological analyte in the liquid based on changes in a shape of a chemical sensing Id-Vgs curve relative to a reference Id-Vgs, in response to the presence of the biological analyte in the liquid on or over the channels of the individual gFETs; the system further comprising a processor configured to read digitized signals from the individual gFETs to respectively determine one or more parameters of the one or more biological analytes in the liquid based on changes in the shape of the chemical sensing I_(d)-V_(gs) curve relative to the reference I_(d)-V_(gs), in response to the presence of the analyte in the liquid on or over the graphene channel of the individual gFETs.
 15. The system of claim 14, wherein the changes in the shape of the chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs) include transconductance slope changes.
 16. The system of claim 15, wherein the transconductance slope changes include changes to transconductance slope in both a p-type region and an n-type region of the chemical sensing I_(d)-V_(gs) curve.
 17. The system of claim 16, wherein the individual gFETs are configured to enable sensing of one or more parameters of the one or more biological analytes in the liquid based on shifts of a chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs), the shifts selected from horizontal shifts, vertical shifts, or combinations thereof.
 18. The system of claim 17, wherein the shifts of the chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs) include shifts in parameters selected from on current (I_(on)) in the p-type region, Dirac voltage (V_(Dirac)), on current (I_(on)) in the n-type region, and combinations thereof.
 19. The system of claim 14, further comprising one or more capture regions on or over the channel of the one or more gFETs, the individual capture regions configured respectively to accommodate attachment of a selected biomaterial to a top surface of the graphene channel, the biomaterial selected to detect a biological analyte of the one or more biological analytes in the liquid.
 20. A method comprising: providing a biosensor integrated circuit (IC) chip having a plurality of well structures configured to receive a liquid comprising one or more biological analytes, the chip comprising a passivation layer with an opening over one or more graphene field effect transistors (gFETs), the individual gFETs comprising: a graphene channel comprising a two-dimensional layer of carbon atoms; a capture region on or over the graphene channel and configured to selectively capture a first analyte or a second analyte of the one or more biological analytes; a conductive drain connected to a first end of the graphene channel; and a conductive source connected to a second end of the graphene channel, the biosensor IC chip further having one or more reference electrodes formed in corresponding metal layer portions of the biosensor IC chip and disposed at a horizontal distance apart from the graphene channels of the one or more gFETs and configured to apply and/or measure a liquid gate voltage to a liquid confined above a top surface of the graphene channels; sensing one or more parameters of the one or more analytes in the liquid based on changes in a shape of a chemical sensing I_(d)-V_(gs) curve relative to a reference I_(d)-V_(gs), in response to the presence of the first analyte or the second analyte in the liquid gate being captured on or over the graphene; and determining differences between the first analyte and the second analyte based on transconductance slope differences of the respective chemical sensing I_(d)-V_(gs) curves. 